MSI K8N Diamond - start problems every second time

Hi.
I have recently had my MB replaced due to failure(total blackout), but I
have run into new problems with the new MB one also.

Every second time I start up the machine, it won't start up past the
second post screen. When the startup windows for win xp is going to show
up, my screen turns black/grey (lcd), and no boot screen for win xp will
show. There it stays, so I'll have to press powerbutton and hold to shut
down. When I start it next, it shows screen for machine boot error last
time and select boot options... boot standard select start windows as
normal and counting down...
And from there it's all fine -until next time i shall start up.

I have tried with out 1 and 1 ram chip and tried the different slots, i
have unplugged dvd burner and floppy, and I have tried a different
graphic card. I have also tried another HD with an old and different
machines win xp installation. Exactly the same flaw every time.
I have reset bios, and loaded failsafe defaults.

Suggestions anyone?

Best regards
Tony