Video Capture - Computer dhuts down

I have tried three different video capture programs and I
geta system shutdown and reboot after around one gig is
captured. Any ideas?

I'm using a video tape machine into a ADS Instant DVD. I
get the recording going OK but after 30 to 30 minutes, the
computer suddenly shuts down - no warning. The wierd
thing is that what I captured is fine. The problem is
that I'm trying to capture a 50 minute video.

I've got plenty of memory, a 2G computer so it is not even
sweating. Any ideas?