Random Virus Appears and Disappears - Help

[rue]

I really don't know what happend. I wasn't doing anything. Just browsing some sites, not even downloading anything. Then, all of the sudden, there's some "System Shutdown" notice/tab on my menu bar. I was wondering what it was, so I clicked on it. No right-click menu. No window. Just a tab, like it was permanently minimized. I tried looking for in in the Windows Task Manager Processes, but there were no odd programs running. It DID show up, however, in the Applications. I tried closing it there, but it didn't work. So, I tried shutting down my computer, I thought my computer just automatically wanted to restart for some reason. All of the sudden, the screen was black, and there was some error message, something about a virus. I was in shock so I didn't really remember anything, just that it was about a virus.

So, in complete fear, I hit the off switch on my power supplier to turn off the computer. Turning it back on, it started out normally, but before I can get to the Windows 2000 greeting screen, there was an error message. It was in a red or crimson box with yellow, gold, or orange borders and text. It said something about Trend ChipAway Virus detected some sort of thing, some sort of virus, and there were two options for me, to insert a floppy disk to restart, or go on as normal. There were other sub-options as well, but I didn't bother checking it out. That exact notice box seemed odd to me because on the bottom right corner, there was a "................" there and it had this little box that was moving left and right, like it was loading or waiting. The box looked like a rectangular box like "[]", except with a smiley face.

Anyway, without a floppy disk, I chose to boot my computer as usual. After signing in, I hit the CTRL+DEL+ALT button and cancelled the Explorer from loading so everything would just stop loading all together, a trick I picked up in the past just incase there were any viruses that loaded during start-up. So far, I've ran my Yahoo! Online Protection program, deleted some trojans and stuff, and I also ran Spybot. So far I've deleted alot of bad things from my computer, and since starting up, I haven't seen anything unusual or out of the norm. It's as if nothing happend.

What exactly happend here? Am I in trouble? Should I be worried?

[rue]

Update: After writing this, I tried restarting my computer. No error messages before restarting this time, but when booting up, it gave me the same error message, the red box with yellow borders and text. It said something about Trend ChipAway Virus has detected a "boot virus", or something. I just remember the word "boot virus", which would make sense since the computer was shutting down earlier. So how can I get rid of this "boot virus"? Is it serious?

Update: I just read about "boot sector viruses" and supposedly you can only get one from a bad floppy or disk? I've never used my floppy drive (probably ever) and haven't inserted any disks in a long, long while. So I guess what I have ISN'T a "boot sector virus"? I would really like to know if I should be alarmed.

Also, I have a few photos and videos I'd like to get out just incase there IS a virus rotting my computer and infecting it. Would it be wise to buy some sort of small harddrive and import my videos and pics there?