Hello,
I hope this posting might save other newbies those hours I had to spend to find the surprising solution.
In short: watch out for the transfer mode configuration of your FTP-client. Make sure "*.php" files are transfered as ASCII instead of binary.
What had happened? I installed Drupal 6.3. Everything went fine. Some days later I uploaded an additional theme (and I happened to do this with a different ftp-client). Then in the Theme Manager side I clicked on "enable" and "Default", then on "Save configuration".
Afterwards I couldn't access any pages. This was the "White side of Death" WSOD (just blank page). I couldn't even go to any page where I could switch back to the former default theme "Garland".
I did heavy searches here at drupal.org. Here some of the words I was searching for (perhaps somebody finds this message because he tries similiar words):
- WSOD, white side of death
- error after installing new theme
- administer, themes, enabled, enable, default, save configuration,
- (and I think quite some more).
I learned that sometimes WSOD may occur because of not enough memory, so I checked this. Didn't seem to be the problem.
After some time I found a workaround to get going again:
http://drupal.org/node/258202