"500 Internal Server Error" after updating 7.14 to 7.24

Though I've off and on "played" with Drupal, I am only a newbie fascinated with Drupal and trying to get it to work. I've been successful at putting up various sites over the years through much trial and error and help from the community. I'm now coming back to Drupal...

I've had difficulty getting the core 7.24 Drupal download to work. I'm not sure I followed the directions accurately in terms of manually editing the .htaccess file (see below). I've searched quite a bit to identify possible solutions and now I'm at a dead end, and am having similar issues as other posters on this thread.

I'm on a shared hosting environment with the following details (and I will be shifting to a Drupal friendly ISP in the New Year):

PHP 5.3
MySQL 5.5.32
mod_rewrite loaded on server
i do have access to my tmp folder

I've already asked and I'm told the memory limit has been upped to 256MB (I just asked for it to be increased, and that's what they told me).

I ran into the "500 Internal Server Error" when getting to the last step of the installation. After much searching, I contacted my ISP and tried to get help there. The technician upped the memory, and nothing immediately changed. When I went back to refresh after a few minutes, my site suddenly appeared and I was able to access the admin functions. I wasn't sure what changed.

When I went to configure the site and enable clean urls, I discovered that I could not enable them, and that one possible solution was to edit the .htaccess file. When I opened my public_html file, I found that the .htaccess file had been renamed to .htaccess_old and that it was basically removed from serving its purpose. At the same time, the site was functional. In the moment I put the .htaccess file back into commission, the site broke. I am unable to figure out what portion of the .htaccess file contributed to the break. However, after searching the Drupal site, I thought it might be that mod_rewrite was not loaded on the server. ISP staff confirmed that it is loaded.

Any thoughts about what might be breaking the site (and how to get the core modules up and running?

Thanks in advance,
Eva

I'm not sure I followed the directions correctly for editing the .htaccess file with the snippets that needed to be manually added to public .htaccess, the tmp, and file .htaccess (the following is public .htaccess):

# Apache/PHP/Drupal settings:
#
# Turn off all options we don't need.
#Options None
#Options +FollowSymLinks

# Set the catch-all handler to prevent scripts from being executed.
SetHandler Drupal_Security_Do_Not_Remove_See_SA_2006_006

  # Override the handler again if we're run later in the evaluation list.
 SetHandler Drupal_Security_Do_Not_Remove_See_SA_2013_003


# If we know how to do it safely, disable the PHP engine entirely.

  php_flag engine off

# Protect files and directories from prying eyes.
<FilesMatch "\.(engine|inc|info|install|make|module|profile|test|po|sh|.*sql|theme|tpl(\.php)?|xtmpl)(~|\.sw[op]|\.bak|\.orig|\.save)?$|^(\..*|Entries.*|Repository|Root|Tag|Template)$|^#.*#$|\.php(~|\.sw[op]|\.bak|\.orig\.save)$">
  Order allow,deny
</FilesMatch>

# Don't show directory listings for URLs which map to a directory.
Options -Indexes

# Follow symbolic links in this directory.
#Options +FollowSymLinks

# Make Drupal handle any 404 errors.
ErrorDocument 404 /index.php

# Set the default handler.
DirectoryIndex index.php index.html index.htm

# Override PHP settings that cannot be changed at runtime. See
# sites/default/default.settings.php and drupal_environment_initialize() in
# includes/bootstrap.inc for settings that can be changed at runtime.
php_value memory_limit 256M

# PHP 5, Apache 1 and 2.
<IfModule mod_php5.c>
  php_flag magic_quotes_gpc                 off
  php_flag magic_quotes_sybase              off
  php_flag register_globals                 off
  php_flag session.auto_start               off
  php_value mbstring.http_input             pass
  php_value mbstring.http_output            pass
  php_flag mbstring.encoding_translation    off
</IfModule>

# Requires mod_expires to be enabled.
<IfModule mod_expires.c>
  # Enable expirations.
  ExpiresActive On

  # Cache all files for 2 weeks after access (A).
  ExpiresDefault A1209600

  <FilesMatch \.php$>
    # Do not allow PHP scripts to be cached unless they explicitly send cache
    # headers themselves. Otherwise all scripts would have to overwrite the
    # headers set by mod_expires if they want another caching behavior. This may
    # fail if an error occurs early in the bootstrap process, and it may cause
    # problems if a non-Drupal PHP file is installed in a subdirectory.
    ExpiresActive Off
  </FilesMatch>
</IfModule>

# Various rewrite rules.
<IfModule mod_rewrite.c>
  RewriteEngine on

  # Set "protossl" to "s" if we were accessed via https://.  This is used later
  # if you enable "www." stripping or enforcement, in order to ensure that
  # you don't bounce between http and https.
  RewriteRule ^ - [E=protossl]
  RewriteCond %{HTTPS} on
  RewriteRule ^ - [E=protossl:s]

  # Make sure Authorization HTTP header is available to PHP
  # even when running as CGI or FastCGI.
  RewriteRule ^ - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

  # Block access to "hidden" directories whose names begin with a period. This
  # includes directories used by version control systems such as Subversion or
  # Git to store control files. Files whose names begin with a period, as well
  # as the control files used by CVS, are protected by the FilesMatch directive
  # above.
  #
  # NOTE: This only works when mod_rewrite is loaded. Without mod_rewrite, it is
  # not possible to block access to entire directories from .htaccess, because
  # <DirectoryMatch> is not allowed here.
  #
  # If you do not have mod_rewrite installed, you should remove these
  # directories from your webroot or otherwise protect them from being
  # downloaded.
  RewriteRule "(^|/)\." - [F]

  # If your site can be accessed both with and without the 'www.' prefix, you
  # can use one of the following settings to redirect users to your preferred
  # URL, either WITH or WITHOUT the 'www.' prefix. Choose ONLY one option:
  #
  # To redirect all users to access the site WITH the 'www.' prefix,
  # (http://example.com/... will be redirected to http://www.example.com/...)
  # uncomment the following:
  # RewriteCond %{HTTP_HOST} .
  # RewriteCond %{HTTP_HOST} !^www\. [NC]
  # RewriteRule ^ http%{ENV:protossl}://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
  #
  # To redirect all users to access the site WITHOUT the 'www.' prefix,
  # (http://www.example.com/... will be redirected to http://example.com/...)
  # uncomment the following:
  # RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
  # RewriteRule ^ http%{ENV:protossl}://%1%{REQUEST_URI} [L,R=301]

  # Modify the RewriteBase if you are using Drupal in a subdirectory or in a
  # VirtualDocumentRoot and the rewrite rules are not working properly.
  # For example if your site is at http://example.com/drupal uncomment and
  # modify the following line:
  # RewriteBase /drupal
  #
  # If your site is running in a VirtualDocumentRoot at http://example.com/,
  # uncomment the following line:
  #RewriteBase /

  # Pass all requests not referring directly to files in the filesystem to
  # index.php. Clean URLs are handled in drupal_environment_initialize().
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_URI} !=/favicon.ico
  RewriteRule ^ index.php [L]

  # Rules to correctly serve gzip compressed CSS and JS files.
  # Requires both mod_rewrite and mod_headers to be enabled.
  <IfModule mod_headers.c>
    # Serve gzip compressed CSS files if they exist and the client accepts gzip.
    RewriteCond %{HTTP:Accept-encoding} gzip
    RewriteCond %{REQUEST_FILENAME}\.gz -s
    RewriteRule ^(.*)\.css $1\.css\.gz [QSA]

    # Serve gzip compressed JS files if they exist and the client accepts gzip.
    RewriteCond %{HTTP:Accept-encoding} gzip
    RewriteCond %{REQUEST_FILENAME}\.gz -s
    RewriteRule ^(.*)\.js $1\.js\.gz [QSA]

    # Serve correct content types, and prevent mod_deflate double gzip.
    RewriteRule \.css\.gz$ - [T=text/css,E=no-gzip:1]
    RewriteRule \.js\.gz$ - [T=text/javascript,E=no-gzip:1]

    <FilesMatch "(\.js\.gz|\.css\.gz)$">
      # Serve correct encoding type.
      Header set Content-Encoding gzip
      # Force proxies to cache gzipped & non-gzipped css/js files separately.
      Header append Vary Accept-Encoding
    </FilesMatch>
  </IfModule>
</IfModule>