Maximum PC

Been a while since I've had to post here for help.
So, the system:
cpu: Intel 2600K
motherboard: ASRock P67 EXTREME4 GEN3
primary hd: OCZ Agility 3 AGT3-25SAT3-120G 2.5" 120GB
memory: gskill ripjaws 8gb
video card: Gigabyte HD 7970
psu: SeaSonic Strider 1000W (yes it is overkill. It was left over from a previous build that needed that much power.)
Recently when booting the usb mouse and keyboard wouldn't power up. Usually a reboot would 'cure' it.
Yesterday when I powered up I got this: Reboot and Select Proper Boot Device or Insert Media in Boot Device and Press a Key
Wasn't sure if it was the motherboard or the drive but I figured it could be a corrupted MBR. So I used the OS disc to do a system repair. That seemed to 'fix' it. But it may just have been the reboot that worked.
Then I started my computer again this morning only to get the same error message. Now I'm thinking more along the lines that it may be the motherboard going flaky on me.
I may be doing some wishful thinking but I'll ask. Does anyone know of some software the could check the motherboard?
I've checked the ASRRock site and didn't find any utilities to do so.

Anytime I have ever received different errors in a system in that short of a time, I always suspect the motherboard. One question: Do you have the latest BIOS revision for this mobo installed? If not, I would try that first. Another thing you might try is inserting a fresh CMOS battery on the motherboard.

BIOS is the latest.
I've never had a motherboard long enough to have the battery fail. This 'board is less than a year old so I doubt the battery is the fault.
But, yes, I know, electronics and batteries can fail at any time.
I've also posted this problem with ASRock Tech Support. I wonder what they will say?

When I see behavior like that in a PC, I usually yank the HD data cable, and boot the system to a Ubuntu (linux) Live CD.

If the Live CD runs fine, I start looking at it as a hosed OS, hosed HD, or occasionally just a SATA cable gone bad.

If the Live CD also gets you a messed up boot, I would (in no special order)

turn down any overclocking
test the RAM
reset the CMOS to defaults
try and boot up with No keyboard (a stuck key can cause nightmares)
unplug the optical drive power cable or anything else that could cause a weird load on your power supply
unplug any other USB devices like printers or headsets
make sure the motherboard has a working speaker - in case it is throwing out beep-codes on boot up

So now, since I posted this here, it has returned to normalcy.
Boots normally, mouse and keyboard power up on boot, no error messages.
Ain't that always the way it goes.
I'll be keeping an eye on it but hope that whatever was wrong sorted itself out. We'll see.