Resolved Acer Veriton M460's Shutting down

[Am not sure I have posted this in the right place]
I am in one office, that has various brands and models of PCs (Dell, IBM, Acer, HP...) on a peer-to-peer network. All 4 PCs of one brand and model - Acer Veriton M460 are behaving (or is it misbehaving) in the same manner. They start well but shut down abruptly. No pattern established yet. Starting them again is a problem as one has to power on/off several times. I have been trying to start this one for the past 30 minutes with no luck - it has now started. They are all running Windows XP SP3, 1GB RAM, Pentium(R) Dual CPU 2.00GHz. There are two Acer Aspire AX3910 (Win 7) that are not affected. Any clues?

 

I opened the PCs and blew out the dust. One is back to normal, the rest are still behaving badly.

 

sounds like power supply to me too

 

I returned one to the supplier - they replaced some components on the motherboad - I think capacitors. It is back to normal. The third computer has failed completely - Windows XP starts up to the logo with the black background. I tried a windows repair - no luck. I have sent it to the workshop.

 

As posted earlier - one computer was restored by blowing the dust out, the rest had capacitors on the motherboard replaced.