Optiplex GX270 - No power

Hi

I have been given a Optiplex GX270 that wont power up. Is there anyway of confirming if the lack of power is caused by the Power Supply or the Motherboard? The previous owner knew very little about computers and told me that this computer only needed formating.

 

When I press the power button I can hear the fan start up then shut down, maybe 2 seconds in total. The power button is orange for that time.

 

The GX270 had a 3hr car trip before I got it home, so the first thing I checked was that the cables and cards were seated correctly. I took the 4 memory cards out and reseated them. The 4 diagnositic lights on the back show no sign of life, but there is a small orange light in the middle of the motherboard that is on. I also had a quick  look at the capacitors on the motherboard, all appear ok.

Would I be safe in assuming that this is a dead power supply?

Cheers Mark