Mac Pro radomly will not turn on..help!

[ericavid]

This is happening every time I shut down the mac pro and leave it off for a few hours. Does not happen on restart or if I shut down just for a few minutes.

After a few hours when I press the power button the white light does not come on but the fans startup and a few seconds later a very fast and short beep sounds and everything shuts down.

If I press the power button again the same thing happens.

If I remove the power cord and reset SMC everything goes back to normal, but not always.

Why is this happening all the time ?? How can I fix this ??

already took apart and cleaned it, sprayed it with contact cleaner, etc.

My specs
Mac Pro 2 X 2.8 Quad
14 GB RAM
4 x 1 TB HD internal
1 ATI Radeon 3870
1 Nvidia GT 120
1 30" Cinema
2 18" NEC

 

[Ommid]

If I was you I would do the following, strip it down as much as possible

i.e. only one pair of ram sticks, only one graphics card, and add bits as you go along and see what happens, might be a problem with some of the ram etc

Added anything recently?

 

[nanofrog]

This could also be a PSU going bad (i.e. capacitors are failing).