It's likely the RAM. But I would check one thing first.
Download Prime95 and RealTemp (links found in Step 10 of the "Step-by-Step Guide to Building a PC" sticky). Install them and run them at the same time. Let it run for at least an hour. Come back with the maximum temps.
Next, go to memtest.org and download the ISO file of MemTest86+. Burn it to CD. Then reboot and enter BIOS. Check the RAM settings against the manufacturer's specs for the exact sticks. It's EXTREMELY important to make sure the settings are EXACTLY the same. Then set the boot order to boot from the CD. Reboot and let it run overnight or through at least 7 passes. I'm willing to bet you get an error.