HellFireXS

I would like to know if this is a RAM issue or a Motherboard Issue:

My computer has been restarting (crashing) it self when Installing windows, Copying files and Playing games (I can no longer copy files or play game because windows isn't installed, I formatted because I thought it was a software problem)

I removed one stick of ram (each stick is 1 GB) and it no longer crashed and windows started to install fine, then I switched the sticks and again no crash, so I put stick one in slot 2 and stick two in slot 1 and it crashed again.

It started months ago and I stopped using it for a while (I assumed it was software related and in need of a format) and bought some new parts for it (Video Cards, Sound Card and Hard Drive) but now when installing windows it will restart in the middle of it and force to start the install process again.

It ran for a good year with no problems and then it started, mostly when copying files, not tiny files but usually larger ones and it also happened when I tried to play a game it would play for a little while and then instant restart

My Specs:
POWER SUPPLY
PC Power and Cooling Turbo-Cool 510 SLI Express
MOTHER BOARD
Asus P5ND2-SLI Deluxe nForce4 S775 1066FSB 4xDDR2 2PCI-Ex16 2PCI-Ex1 3PCI SATA300-R ATA-R 2x i1394 USB2.0 7.1Audio 2x G-LAN ATX
CPU
Intel PentiumD 3.0GHz 830 Dual-Core 800FSB 2MB L2 Cache Socket 775
RAM 1
Infineon 1024M DDR2-533 PC2-4200 SDRAM
RAM 2
Infineon 1024M DDR2-533 PC2-4200 SDRAM
VIDEO CARD 1
eVGA nVidia GeForce 7950 GT KO 512MB PCI-Express x16 N635 w/ Dual-DVI-I / HDTV-Out
VIDEO CARD 2
eVGA nVidia GeForce 7950 GT KO 512MB PCI-Express x16 N635 w/ Dual-DVI-I / HDTV-Out
SOUND CARD
Creative Labs Sound Blaster Audigy SE 7.1 PCI 24-bit Sound Card w/ 96KHz Surround (OEM)
HARD DRIVE
Seagate Barracuda 320GB 7200RPM SATA-II-300 3.5" w/ 8MB