when i boot up the pc , it will be shut down in about 10 sec. I cleaned up the cpu heatsink and the problem is still there.

Graphical Card :XFX Nvidia Geforce 7300GT/256/PCI-E

Power Supply: Cooler Master 430W extreme power

Mother Board: Msi 945GZM3

CPU: LGA-2.8 GHZ- DUal core

Ram: DDR2 kingston Ram

HardDIsk: samsung 160gb sata HDD

When did this start to happen? Some history might help us help.

Was it all OK for ever and ever then one day just out of the blue etc.?

Hmm it was okay at 1st until i add in one addition ram into the ram slot and when i try to start the pc it started to shut down. i removed the hdd / cd-rom and ram and the problem is still there.

Sounds like incompatible RAM.

I'd suggest returning the hardware configuration to as it was before the RAM change then clear the CMOS.

Instructions on how to clear the CMOS should be in your motherboard manual.

After clearing the CMOS and with just the old hardware installed see if it will work.

Nope the problem still exist after i reset the cmos and return it to the old hardware installed.

Can you get into the BIOS Setup?

Nope before i try to get in the pc auto shut down.

I'd suggest re-doing all your connections.

In other words disconnect everything and rebuild.

If the Clear CMOS did not involve removing the battery than remove the battery for a few minutes as well then re-insert.

Testing the PSU would also be useful:

Just for example:

FrozenCPU ATX 2.0 Ultimate LCD Power Supply Tester (20/24 pin ATX, SATA, P4, Xeon, PCI-E, Floppy, 4 pin) - FrozenCPU.com

hmm i don have the PSU tester kit. I try rebuild and reconnect the wires.

same prob still, even though i reconnect everything.