Doesn't matter if my son is playing a video game on hotweels.com, or if I'm watching a video on youtube. Doesn't matter if other applications are open or not. It will play for a few minutes then the PC just shuts off, like you pressed the power button. No warning whatsoever, doesn't say anything about "system shutting down" like when you typically shut down Windows. We have to leave it off for about 10 minutes or so (maybe less, but have found 1 minute doesn't do the trick) in order to boot it up again.
The only thing different we did that I know of was switch from Dish Network to AT&T uVerse, so now using AT&T equipment. This issue seems to have started around the same time, but not 100% sure if it happened a day or 2 before we switched to uVerse.
Windows XP version 2002, SP 3
Pentium® 4 CPU 3.20GHz
3.20 GHz, 2.00 GB RAM