Computer Problem! EEK!

My Finder crashed yesterday! I tried to download a friend's book she's been writing because she asked me to review it for her, but it seems like the file is corrupt! Its crashed my finder completely, it refuses to open or respond to Force Quit - Relaunch! I've tried pretty much everything, my Trash Bin refuses to open as well, I am unable to open and empty Trash or look at my Finder. I tried to make a new Account on my computer, but my Accounts pane in system preferences also will not open or respond. I am still able to use every other Application on my computer, except the ones I've mentioned. I have no idea what to do, someone help me, I really don't want to have to take my computer to the store itself to be fixed.

Thanks Guys, sorry for not posting in forever, I'll try to make it up somehow.