I Have fitted a new motherboard (MSI K9AGM2) toegether with an AMD Sempron cpu and 1 gig ram purchased as a package. The unit booted up but while I was in setup keying in date and time everything shutdown (unit ran for 5 mnutes). Now when I try to start it goes for 1 to 2 seconds then everything shuts down including fan on power supply. If i unplug the Jpw1 (power for cpu) it keeps running ok and doesn't switch off without the cpu. Heat sink checked and reset - doesn't seem to be hot and couldn't in 1 second. Have unpluged power to hard drive and cd but that doesn't change it. Must be something switching everything off at startup. Any idea's??

Make sure you have connected that 4, 6 or 8 pin power connector from the power supply to the motherboard near the CPU

Yep its a 4 pin power plug that runs the cpu. When it's pluged in everything shuts down after 2 secs and when it's not the fans, hard drive and power supply keep running.

Faulty V-rails on the psu?
Do you have another psu you can try, its always the cheapest solution. A 300w should be fine for your rig. If it still shuts down, i'd RMA the motherboard.

Double check every connection by removing and reseating all memory, cables, etc. Something fundamental and basic is out of whack. If it is truly only running for 2 seconds, I would suspect the power supply, memory, or video graphics.
What happens when you cold boot in SAFE MODE?

Good possibility your heatsink isn't making good contact with the cpu.

I put the multi meter on the cpu power plug connections and I get 26 volts. Manual says it should be 12 volts. PSU might be the problem.

Interesting. Please keep us posted.

If you have applied 26 volts to a 12 volt circuit, the motherboard/CPU may be fried

Was this and older case with PSU? What's the rating on the PSU in terms of Watts and Volts.. I know you said a volt meter was use to tell you 26volts..

The PSU is a 430 watt Thermaltake. The PSU and case are a year old and used to build up a unit which never ran. So I repaced the motherboad and cpu. I used a multi meter to check the voltage on the four pin power plug for the cpu.

I have replaced the power suppy plus the mother board and the cpu again and it's running fine

Thank you for the update. It is always great to learn what really happened.

yahh lol exactly ray i wish every1 did this instead of leaving us in the air