did you install any browser plugins recently?
I'd go through your browser preferences (settings) and make sure that you have both cookies and scripts (javascript) enabled. If you are using a script-blocking plugin for security, you probably need to turn that off for PentaxForums.
Good luck!
Edit: oh and if all else fails, download a new browser. Both (
http://www.mozilla.com/firefox or
http://opera.com are free for personal use.