Dell Optiplex GX280

That series(gx240-gx280) was notorious for bad capacitors on the motherboards and bad power supplies. I would suspect those first, there will be a line of LED lights on the back near the I/O ports, what are they displaying? Is the power LED green or orange? Is the PC emitting a beep code?


Let me know and we can narrow it down.

Regards,

Lordy123

The first thing to check is the power supply. Test it or try replacing it.

I agree with Lordy123.  It sounds like Capacitor Plague:

http://en.wikipedia.org/wiki/Capacitor_plague

Tried other PSU  & capacitors look good , no swelling  of indication thereof or even sign of a burnt cap

Whats the status of the LEDs by the I/O ports? What about the front LED?

try resetting the bios
how : remove AC cord -  then remove bios battery for a minitue.
reconnect all and test
you can use this guide also  : http://www.experts-exchange.com/articles/Hardware/Components/Motherboards/Short-overview-of-how-to-troubleshoot-bad-hardware-when-a-pc-does-not-post.htm

I have seen this in a couple of GX280s and, judging from postings here over the past year or so, this model was apparently notorious for this specific problem.  Troubleshooting with a POST 4 card produced both no, and inconsistent, results.  I was never able to find a satisfactory solution, and ended up recommending that the customer replace them with a more reliable platform.