[support] Drupal 5.7 - cannot update nodes

Hi, I've run into a strange problem on a small personal blog. When I edit a node (any node) and submit it, I get redirected to the frontpage and the node I was editing is not updated. No errors in drupal's log or in the server logs (though they do not log mysql errors).

The strange thing is that I can create new nodes but then I still can't edit them (the changes are not saved). Revisions are enabled, but I've tried disabling them with no luck.

Any suggestions? Maybe somebody knows what could be wrong? The site worked fine for some time. No major changes were made before this happened (just editing menu items, nodes).

Thanks in advance, Domas