What happened? I can probably tell you how to fix it.
(Huge Edit)
Okay, i'll tell you what happened. For some weird assed reason, the layers, filters, and edit menus were all greyed out. As well, most of my tools could not be used, I couldnt do anything, literally. As I mentioned, i tried reinstalling, and all that crap, much to no avail. I'm not sure if it was something I did, because I did nothing out of the ordinary, and i've never run into this type of problem before... I just tried system restore, but that didnt fix it (AND for some odd reason, my list of filters was significantly smaller. I had no blurs, few distorts, a couple of stylizes and thats it, and they were stilled greyed out. So I undid that restore, and I have my filters back... though still greyed out.)
This is quite annoying, I dont know how it started or how to fix it... I cant even finish the project I have been working on for ages ;_; (huge edit)
Make sure the image mode of whatever you were working on isn't in 16-bits/channel. That will grey out a bunch of the filters and such.