OK, so everything is brand-new. This means to me that there was never a time when everything was working properly together, so it's time to start ruling things out.
Hard Drives, Part 1: Disable the RAID. Only connect one drive in single-mode if possible. I don't know how you set up things, but this may not be as impossible as it sounds.
Hard Drives Part 2: As has been mentioned, each manufacturer has a diagnostics program that can thoroughly diagnose drives that are acting wonky. A good test will take overnight - time to spend some nights testing them. You may have to disconnect the RAID in order to test this way.
Power Supply: Though I prefer to get a power supply tester dongle ($15 at any good PC store, or even compusa) and a multimeter to really verify output voltages, the free program Speedfan lists voltages (and other stuf too) reliably. It can also chart changes over time, which is handy when troubleshooting. Look for low voltages.
This is also good for testing that the CPU isn't overheating and that the fans are spinning. Check it.
RAM: Memtest86 is very reliable. It also comes on almost any bootable Linux CD: just pay attention to the start menu when the CD boots and choose Memtest86, and let it run overnight.
While you're at it, if you download a bootable linux disk like Ubuntu, you may want to run Linux from it for a day or two and see how it acts. If it works just fine, that's a good indication that the hardware is fine. If it starts acting wonky, then the hardware may be suspect somewhere.
CPU: Tough to test reliably, in my experience. This site (
http://www.benchmarkhq.ru/english.html?/be_cpu.html) has lots of testing programs to make a CPU get hot, among others. If you can get a few of these apps to run reliably, then your CPU is probably OK. Use Speedfan with these apps to check for overheating.
Mainboard: Other than messed up caps, perhaps you're running at an incorrect bus speed? Memory timings too fast? Try throttling down some settings and see what happens.
House Electrical Power: If you have a spare UPS (battery backup thingie) liying around, time to use it. I can't tell you how many mysterious hardware failures I have personally solved with a good APC brand UPS. Anything under $100 will do - the goal is to filter power and supply enough to keep it running for a microsecond with weak house power, rather than half an hour.
So, we've left you with a few evening's work. Let us know.
-Llama
