Comp freeze, win media player, any video

Ok so.
My bf made my computer, got all the good parts, everything put in perfectly. It works great. A majority of the time I play mmo online games, and I rarely use the computer for anything else.

Everyonce in awhile I will watch movie trailers from apple, videos from forums for my game and they came in great and wonderful.

About 5 months into using the computer it started freezing whenever I clicked on a video. I made sure wmp(windows media player) was selected for all file types. Still, everytime I clicked on the link, the wmp came up and basically, the machine started to go realllllly slow, the screen would blink, the mouse would move slow and I could not alt tab, altcntrldelete out of it. I had to just reboot it with the button.

So I scanned for viruses, reinstalled drivers, got update drivers. I finally resorted to reformatting.

I reformated, and tried it after all the drivers were updated, and bingo. It worked. ..... for about 2 weeks.
Then same thing started happening again.
I started using my bf's computer and played the same games, went to the same sites, and did nothing differently just to make sure it wasn't me.
Nothing happened to use so he figured maybe it was the video card.
He went out and got a new, even better video card. Updated drivers, got java, directx, divx, everything... and still not working.

It does play YouTube videos though... oddly enough =/
But nothing that streams or buffers... =/
HELP plz

Here are the computer facts:
AMD Athlon 64 processor 3700+ ~2.2 ghz
2048MB Ram

My new card is:
NVIDIA geforce 7600 GS total memory on it 512 mb ram

thanks