I have an original Mac Mini that I've recently repurposed for a media center. Right now I have it connected to an external HD and an EyeTV (which is actually unchanged from before; the only difference now is that it's hooked up to my TV via a DVI-RCA plug). The day after I made the change, it started going to sleep for no obvious reason. When watching EyeTV it seems to be fine, but after playing a video (AVI, MP4, etc.) for 10-15 minutes it will sleep.
It does this in MediaCentral, iTunes, and VLC, so I don't think the problem is on the HW side. I thought it might be overheating, but it also seems strange that it's doing it all of a sudden.
Any ideas?