doing a google search on your problem leads to all the other boards where you've posted; so I've seen those replies as well

perhaps all I can offer is a new track ...

your computer runs fine for 10 - 12 hours ... THEN LOCKS ?
you have to manualy power off?
can you immeadiatly re-start?
it is always 10 - 12 hours?

no errors in the event manager?

your motherboard is ok? does your BIOS have a possible upgrade?

any settings in your BIOS that might be causing this?

is your P III a slot one processor? are the locking tabs secure? (i have seen heat un-seat slot 1 processors)

...still searching

Hello. I have used Security task Manager when my CSRSS.exe spiked and absolutely demolished my use of the internet.
I found a 100% Danger File named bBO cyber bot
I have never seen that name before and the name itself seems very dangerous and suspicious to a computer. So even though it was risky, I destroyed the file. Luckily, instead of getting a system error failure, my suspicious CSRSS.exe stopped spiking and therefore I'm fine now. See if it helps.