After Effects crashes after new hardware..

Hi there :) I got my new computer hardware about a week ago, and I was really excited and all that untill I found out that After Effects didn't work.. Here's my problem: When I import a video file into after effects, like .mov .avi etc. it all works just fine. But when I try to move it into my composition, it freezes, I can't do Anything. I can sit around and wait untill it responds, but impatient me can't sit more than 10 minutes and wait for something to happen.. I mean, it shouldn't take more than 30-40 seconds for it to respond again.. So, what I do is i try to move the movie around in the composition, then it appears "Not Responding" up in the left corner, then it crashes, like "After effects has stopped working, do you want to try to find a solotion or exit", and a solotion does not work.. Note that this is _not_ happening when I drag a hi-res picture into the comp.. Ive tried to reinstall After effects several times, not working. Reinstall Vista, not working.. I have Quicktime 7.3, After effects CS3.

My Computer hardware is:

Gigabyte x38 DS5, f5 BIOS
Intel Core 2 Duo E8400
Gainward 8800GT 512 Mb
3 Gb PC6400 RAM

And it worked before I changed the processor and motherboard..

So, do you guys have any idea why my After Effects wont work? Sorry for my bad english, Im from Sweden.. :)

Thanks in Advance :)