Your power supply could be too wimpy.
What rating and brand is it? That system needs 350W at least with a good name brand power supply (antec, enlight, etc). A cheaper generic or off name brand at least 400W and atht is still no guarantee of adequate power.
You should be able to check the voltages in bios but that will be under very light load. Make sure the % volts is at or above 5 v and the 12v is at or above 12v.
Biggest problem these days is the 5V can't supply enough amps. Everything is beingloaded on the 5V supply taht used to use 12V.
Get a copy of Sisoft Sandra (free version) and check while actually doing something (moving a big file from one sdisk to another, burning a cd etc.).
For a quick experiment drop the ram to 384 or 512, disconnect the second HD and the second CD drive. See if the warning goes away. If it does invest in a decent power supply Antec/Enlight 380W or higher.
PS - Just noticed you have a PNY card. It could be the card. If the voltages look ok and lowering the load doesn't help you got a bum card. If you do return it consider another brand. PNY has a higher than average problem rate.
If it is the card post again asking for GE4 5600 Ultra brand recommendations. I've had problems with Gainward but many others like them. Stay away from MSI (sloppy assembly leading to faults). Xtasy is iff'y. The Powercolor cards I've seen have been very well built.
