"Explorer.exe" Crashing Repeatedly During Games?

So I've recently gotten a problem where my Windows Explorer will crash and then restart whenever I am playing games through Steam. And it's not every game either;just randoms. Sometimes it will happen the moment the game launches, other times it could be 15-20 minutes into playing. I'll get alt-tabbed automatically out of my game to that message and have to wait for it to restart to go back in, very frustrating. This only just started happening less than a month ago and I've been an avid Steam user since I built my first custom PC in February 2011.If I had to pinpoint the time Explorer.exe first started crashing, I'd say shortly after downloading a keygen for a non-Steam game... that i PURCHASED (Yeah, sounds stupid but it's a long story). The keygen seemed suspicious the moment I tried launching it, and nothing happened... so naturally I have followed up with beefing up my anti-virus/spyware defenses and running vigorous full-system scans. Speaking of, Microsoft Security Essentials (which my friend swears by..) just completed an entire scan, which took about 3 hrs to complete, and turned up not a single bad file .

After several virus scans to no serious threats, running CCleaner thoroughly, defragmenting my hard drive, performing that built-in system checker command in Cmd Prompt (can't remember the actual name), I ended up formatting and re-installing Windows 7 altogether. I have all of my games, music, photos, etc on my 1.5TB hard drive, and Windows on my SSD, so It wasn't a big deal. All seemed fine and well until I went to go play some games and then there it was again... then i started noticing every once in a while it would happen even on my desktop just simply browsing the web or something. My video drivers are up to date, I have made sure i'm up-to-date with Windows Update.