Problems with Precision M6400

The screen on my Precision M6400 started going blank. If any audio had been playing, it continued to play, so it seemed to be a display problem. When the problem happened, the only thing that fixed it was rebooting. The problem was getting more frequent.

I had been planning on upgrading the video card and CPU, so I went ahead and did that, thinking that the problem was probably one of those anyway. But that didn't fix the problem.

So I tried a new motherboard. Now the problem is worse.

When I booted up, it prompted me to go into the RAID configuration utility. My drives aren't RAID. In the RAID configuration utility, it told me that I did not have a RAID volume ("Raid Volumes: None Defined)". It does list my two hard drives, and for each of them says that their "Type/Status (Vol ID)" is "Non-RAID Disk".

Instead of going blank, the screen now goes to a single color -- sometimes white, sometimes orange. Sometimes a pulsing white. Once it did go blank. It's doing this so often that the computer is basically unusable for normal use; after booting only goes maybe a minute or so before the problem happens. I'm writing this on another computer.

I looked through the BIOS settings and found that this motherboard had the SATA operation set to RAID. I changed it to AHCI. But then it wouldn't boot. Windows goes into a automated repair procedure, then reboots, then goes into the repair procedure again. It never stops cycling through that. I tried setting SATA operation to ATA, the only other option other than turning it off, and it had the same problem. 

So I set SATA operation back to RAID, and now it boots again, though it's back to going to a single color, sometimes pulsing. 

Any suggestions? Did booting up with SATA operation set to RAID do something to the discs even though the RAID configuration itself says the disks aren't RAID? Given that the disks aren't RAID, why can I boot up with SATA operation set to RAID but not to AHCI (or ATA)?