machine keeps restarting in one location and not another

I have a customer where I have installed 2 identical IBM machines, each with a Core 2 Duo 2.4 GHz processor, 4 GB of ram, fresh install of XPP - SP3, 250 GB HDD. These two machines replaced two older machines, an HP and an IBM which ran OK with the exception of being slow.

I set the two machines up here in my office before installing them in his office. I ran them both for 8 hours a day for 4 days without problem. When they were installed in his office one unit ran perfectly. The other machine ran fine for a few hours. I worked on it transferring data from his old IBM to the new one. After I left he installed Simply Accounting at which point it then began to freeze and restart on its own. I went back and tried a system restore but that didn’t resolve anything.

I hooked up his old IBM machine and took the new machine back to another of my offices (different location) where it ran fine, again for many hours. Thinking that it was the Simply Accounting installation and not knowing what else I might do, I reformatted the machine and reinstalled everything except Simply. It ran fine again for several hours again, over 4 days.

I reinstalled it in his office and it ran fine. I installed Simply Accounting again and it ran fine from last Monday to this Monday morning. The user tried to install his printers on this Monday morning and the machine froze up. Now it is restarting on its own once again. He replaced the machine with his old IBM and it works fine.

Has anyone got any ideas as to why this might be happening? It makes no sense that it would work fine in my two locations and not in his office.

Any assistance will be gratefully appreciated.

 

Thanks Tony, will look see

We are thinking that a UPS is in order here