Newbie built system randomly reboots

[jmurmur]

I was trying to save money and built a system myself. Originally I wanted to reuse as much as I could from my other (fully functional) PC so please don't bash me for the parts here, if I could do it over I would go completely different. I had to get a new MB, HD, RAM and I bought a graphics card.

Setup:
Intel Core Duo e8500 - used from ebay, said was tested good
ASRock G41C-GS R2.0 - new
1 4gb ram (G.skill I think it is) - new
Hitachi 500gb HD - new
Geforce gtx 280 - used from ebay said was tested good
EVGA 500w PS - new
reused the cd & dvd drives I had
Windows 7 home premium - new copy from ebay but came with its own product key

Loaded windows from scratch (new HD) and everything went ok. Found the driver for the GTX280 and tried to load it and PC said no card found, then PC rebooted. Tried googling info about the gtx280 and the pc randomly rebooted a few times before I found out there's a red/green light on the grahics card. Checked and found the light red. Searched a little more and found out that the minimum recommended power for the graphics card is 550w (on GeForce website). I had used a power supply calculator from the internet which is why I chose that wattage, not knowing about the cards requirement. Not sure if this was the problem I powered off system and removed the card. Booted up again and started searching for power supplies 550 and up and it rebooted on me again.

I'm using my old system now but what can I start checking to see what the problem is for all these random reboots?

 

[jmurmur]

I think I have it figured out. I was reading a bunch of threads on here about the same issue. I booted into the bios menu and scrolled till I found the memory section. The memory card had 1.6V grayed out and 1.5V next to it which I could change. I just set it to 'auto' like all the other voltages were and it seems to work fine now.

I also found out that the GTX 280 needs to have both of the PCI-E connectors plugged in to get enough power so I did that and the green light came on but the system would not turn on. Guess that's why it was rated at 550W minimum, my 500W doesn't have enough power to do the card and everything else. I just ordered another card off Ebay that has a low enough power requirement so I shouldn't have this problem anymore.