Sounds a lot like a virus hijacked your PC and corrupted some of your data.
Often times, when you install a program and afterward your computer gets frozen, it's a sign of either incompatibility or malware.
My advice is to make sure you have as much virus protection as possible: Ad-Aware SE, Spybot S&D, Spyware Doctor, Spysweeper, ZoneAlarm, McAffee, etc. I know you mentioned Norton, but sometimes trojans go chiefly after anitvirus software. Tricky, eh?
P.S. Steelers rock.
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