I'm running website using Drupal 7.34 on an external ISP.

It's been up and working fine for a long time, but now I'm suddenly unable to add content (any content type). I can select "Add content", fill out all the information and submit it. But instead of saving it to Drupal, I only get back to a new empty content form.

I do not add content very often, so it might be a month since I actually added something. Since then the only changes I've performed to the installation is regular updates every now and then.

Any suggestions as to how I can debug and solve this?