Random crashes on Desktop/Mainboard at fault?

Hey and thanks for the help in advance:

I have random freezes in windows... Sometimes to black screen,
sometimes just freeze... Sometimes with audio screeching, sometimes not...

Now the weirdest thing: As I reboot, I sometimes got the "Boot Block trying to
read bios from harddisk", suggesting a bad bios to me. Around 1 in 3 times.

It happened first time over-night, when I checked it this morning screens were
black and pc running but crashed... Now it crashes between 5-25 Minutes after
I boot, eventhough it's been real hot the last few days and is cooler today for
the first time...

Whats going on? How can I pinpoint my mainboard as the culprit? Is that a
common problem on the Gigabyte p35 ds3r? If it went tits-up, how do I fix it?


Rundown:
2x1gb ocz ram
p35-ds3r gigabyte mainboard
intel quad
8800gt


PS: I had bad RAM TWICE over the past 4 months, with new modules used all 3 times... Always the same OCZ model on warranty. Maybe that's relevant somehow.