My system has been running like a dream for 6 months, but shortly after adding a second 512Mb ram it started to warn me of a fluctuating 12v supply. ASUS Probe was showing it rising to 13.3v but a few seconds later it would return to normal, and being advised that it wouldn't do any harm, I ignored it. A few days later it crashed and the PSU was diagnosed as the problem and replaced with a 500W unit.
The crashes continued and got progressively worse until now it freezes immediately on Power up - I can just get the BIOS screen up but it freezes before any adjustments can be made.
My IT friends have suggested, in turn, just about every component in the box !!!
I'm told I cannot Flash Bios as the machine isn't staying stable long enough.

Any suggestions fellas??
but shortly after adding a second 512Mb ram : T_Les_H
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Take it out......now what happens....can your mobo handle  EXTRA ram?...how old id this pc?Are you OVERCLOCKING?Thanks for the response merlin_2

I took out the new ram as soon as it started to play up, and I've also swapped and switched them about, but it just got worse and worse - i.e. the crashes came quicker.
The system was built new 6 months AGO and is, or was, used mainly for photo editing, hence the extra ram.
The Spec briefly is;
AMD XP2800, ASUS A7V600-X, Radeon 7000 64Mb, DDR 400 PC3200 Ram, Running XP Pro

And Raptor in answer to your thoughts - No, as I said I was happily running it since new until either the ram or PSU seemed to have caused a disaster.
Do you think that the voltage fluctuation could have damaged the M'Board or CPU?Sorry Raptor, I posted before reading it through
I even slowed the Clock speed down a notch, but it still crashed.Have you tried to reset the BIOS to default values?What the make of the hard drive?? what happens if for agrument sake you place the winxp install disk in the drive.......does it display the  winxp setup screen?on boot up..Sorry for the silence over the last few days, but DOMESTIC chores had to take priority.
I decided to bite the bullet and stripped the whole lot out - well I had looked at it often enough, and there had to be a first time, so I ended up with a bare case.
Put it all back, except for the new Ram and it booted up first time !!! I've set BIOS to default, so I guess it will need a little tweeking, but it's started up 3 times now and run for 5 or 6 hours.
I must now SUMMON up the courage to put the second Ram in and if it plays up again then I guess that must point the finger, but why was it still playing dead when that item was removed ?
I will never understand these Bl***y machines, but thanks for the interest you two guys took in my plight.It's good to know there's help out there.Some ramsticks look the same......i tend  to buy them by pairs of ramsticks of the same make....