Help, can't login to my forum!

[Macsee]

Help!

I had someone work on the htaccess files (the one in root and the one in the forum folder). He had FTP access and access to the forum admin account (I trust him). He shouldn't have made any changes in the admincp except for turning on/off the forcewww plugin.

He sorted all the redirects etc. in the htaccess. I tested them and they all seemed to be working fine and he went away. I may not see him for a few days now.

But I just discovered I can't log in! When I log into the forum at the forum homepage I am just sent back to that homepage with the username and password boxes blanked out. If I fill those boxes out and submit the same thing happens again.

I can't log in to the admincp either. Same problem. But one small (but weird) difference:
If I try and fail to login to the forum - and THEN try to login to admin CP I get straight into the admincp.

But I still don't have a way to login to the forum itself and make posts. The problem seems not exclusive to me and is affecting other users as well.

Any suggestions on what could be causing the above activity would be very gratefully received.