"The Natural Philosopher" wrote in message
...
But a mobo isnt as expensive as the RAM and CPU that goes in it.

But befier that remove all peripehrals 0 disks etc - ram chips and pci
cards etc and see if the psu dies then

Changing a motherboard (unless it is to one of exactly the same type, with
all the same make of devices such as graphics, disk controller, USB
controller etc) may cause the PC to blue screen because the drivers don't
match the devices.

One though that I don't think has been mentioned: is the CPU fan spinning at
full speed? There may be a shutdown (to protect the CPU) is the fan isn't
detected to be running at the right speed. 3 seconds is a bit soon for the
over-temperature sensor in the CPU to kick in, but could be about right for
a fan speed detector.