Definitely post the specs of your PSU. If you're using junky power supplies they might blow out like that.
But if they're perfectly good, brand name, top tier PSU's, I would get the wiring and home power lines checked.

HP Media Center machine
MOBO: ASUS OEM board
CPU: 2.6 GHz Socket AM2 Athlon X2 5000+
RAM: 2 GB Qimonda PC2-4200 DDR2 RAM
GFX: Sapphire Radeon HD 4850
HDD: Seagate Barracuda 320 GB SATA 7200 RPM