I'm having a similar problem with the NV 5000 series card. I have built quite a few systems although some have the problem where they will automatically stop recording. Im using Windows Xp service pack 3 as my OS, and using 7.5 NV software. I also have all my systems standard to what soundman98 has suggested.
I need these Avermedias to be working 24/7 without any problems. Replys and Help would be much appreciated.