blank page upon signing in

when I sign in, all I get is a blank white page (no html at all). I keep refreshing, same blank page. I have to clear my cookies, and only then will the forum show up again, but I'm logged out. I log back in, same blank page.

When I log in through the page given to me when I try to access a members-only feature (like trying to search for something), then I'm taken to the vbulletin mobile version of this forum. I click on the "Full Site" link on the bottom, and THEN now I'm taken to the regular version of the forum when I'm logged in.

So... something you guys should look into. I use Firefox 15.

Same exact problem still.