PC turning off after a few seconds

[Hodsocks]

I have a pc I am looking at which switches itself off after a few seconds, initially when I checked it I noticed that the AM2 processor mount had broken so that the h/s and fan where only secured by one clip. Thinking this lack of cooling would be causing the processor to overheat and trip out the machine I replaced it but am still having the same problem.
After checking all connections and reseating them I noticed that it seemed to stay on if the hard drive was not connected to the psu, thinking it may be a power supply issue I tried a new psu but again still no resolution.
After all of this I am now finding that the machine won't stay on for more than a few seconds whatever I do, it may possibly ne mobo but I'm trying to avoid that conclusion at the moment.
Have any of you guys any suggestions as to what may be causing the problem

 

[Mark56]

If the cooler has detatched from the CPU it is quite likely the CPU has fried.

Is it reaching POST?

 

[Hodsocks]

As I mentioned above it has posted a few times, but most of the time it turns off before posting

 

[Mark56]

Errr, you never used the word POST in you opening question.

As it switches off before POST, most of the time, your CPU is most likely fried. Having no cooler attatched for any length of time is death to a CPU. Every time a boot has been attempted it will have done more damage to the CPU. I think you have to accept it is fried and needs to be replaced.

 

[skipper86]

Make sure that the cooling system of your PC is working fine...!