The usual causes for random shutdowns are:

Overheating triggers auto-shutdown to protect the CPU.
Memory module going bad.
Power supply going bad. ** Most likely culprit
Power unreliable (do your lights flicker? - Brownouts ocurring)
Check energy savings settings in control panel and BIOS.
If you have an Athlon XP Chip and PC133 memory, change the memory.
Some computers shut themselves down automatically if the processor fan stops or stalls. ** Good possibility



>Hi Neil,
>
>I have not checked the Event Logs but I will ( if the machine stays on long enough to let me :-) ). Hopefully the power supply issue will be resolved tomorrow. UPS is not a problem, ran the machine directly from the wall and still shut down. I have some temp checking software that I will run also when i get the chance.
>
>Bill
>
>>Hi,
>>Have you checked the Event logs for pointers to what is going on, if there are no entries check the power supply, check the CPU temp and also check the UPS, the battery could be dead, the software usually has a test mode.
>>
>>>I have been having a problem with my home computer spontaneously shutting down and it is becoming more frequent. Computer will just turn off, no BSOD, no software warnings, just turns off like the power switch was thrown or power cord pulled out of the wall. Machine is ~2 years old, Asus mother board, AMD processor, Win XP Pro SP2 OS. All power options have been turned off to exclude them. Fans were checked to be running, air ports were cleaned and internal parts were cleaned of dust, etc.
>>>
>>>Anyone know the cuase and cure of this?
>>>
>>>Thanks,
>>>Bill