The first thing that comes to mind is a whole lot of temp files and junk. Right-click on C:, Properties, Disk cleanup. See what that does.
Another tactic: Look in Windows/temp. You could delete that entire directory and be ok. Check it out on google first if that's not something you want to do. At least in the 'old days' that used to be a huge repository of crap.
As for identities, I don't know.
"If I'm wearing long pants, I'm too far north" - 2oldman