Problem with my computer

I have a rather strange problem on my computer.
For some reason it slows down incredibly not allowing me to do anything.

This all started for no reason at all, last night I was on it playing a game working all good. This morning, I pressed 'Start', it opened, and then it stayed open forever, and it stayed thinking like crazy. I heard the computer making the thinking noise and the thinking green light keep blinking nonstop. I could not get rid of the Start Menu from being open, or do anything else for that matter.

The same thing happened after 3 times that I restarted.

Finally, I got the problem semi-fixed. So I updated my virus definitions and updates in Norton AntiVirus 2002, scanned for viruses, I was clean, then I scheduled a ScanDisk after I reboot.

I rebooted, and ScanDisk reported an error.

STOP:

    tbcspud.sys (ERROR xxxxx and a bunch of letters and numbers)

ScanDisk could not continue because it shut the computer down to 'prevent further damage'.

Then when I got the computer on, it said 'system recovered from severe error'. So I ran System Restore but I had no restore point, so I could not do it.

Can anyone PLEASE help me? I am usually able to fix my compuer myself, but this has never happened.