KM4M-L problem

My system's power supply (Antec 300 Watt)failed. I replaced the
defective power supply with a good supply, the machine turns on only
long enough for the CPU fan and case fan to begin to spin. Then power
goes away. The system is a MSI KM4M motherboard, AMD Athlon 1800 cpu and
Micron memory. Case is an Antec SLK2600AMB.

What would cause the above symptoms?

Thanks,
Lloyd

Update: A participant on this forum suggested privately, that it might
be a thermal conductivity problem, I reapplied Arctic Silver 3 and
ensured that the heat sink was properly installed. This made no
difference, the system still exhibits the momentary on then shutdown
behavior.

Could the failure of the PS have taken something else with it? I have a
spare CPU, but am loath to swap it in not knowing if it might be killed.


I'd welcome any further suggestions.

Thanks,
Lloyd