I agree with Memtest. www.memtest.org
You can also use the Windows Memory Diagnostic utility which you can just start and reboot. It will just show that you have a hardware error though. I prefer memtest because if you run it for a few hours and the SAME error keeps popping up it's a safe bet it's the memory and not your motherboard whereas the Windows version is too vague.
If you DO show errors:
1. Make sure BIOS is up to date
2. Set both CPU and MEMORY (RAM) to default/stock settings.
3. retest if you changed anything.
If memory has errors at default settings you'll need to RMA it.