PC won't start!!

[Trialsfan]

Hi...hope someone can suggest a reason why my son's desktop will not start?

He was using it the other day and for no apparent reason it decided to just switch off!!When first tried to restart it all he got was a strange sound,a bit like a knocking sound!

When I try to re-start it ,it will not power up.I thought perhaps as it's about 3 yrs old maybe the power supply was at fault but I'm not so sure now, as I opened up the base unit and turned the power on at the wall socket and the fan on the power unit was running also the fan on the graphics card albeit at a slow speed but on pressing the power button on the base nothing happens.

Sorry to be a bit long winded but thought the more detail the easier it might be to diagnose.

Any help much appreciated so thanks in advance.

 

[Trialsfan]

Mr LOL...thanks for your quick reply.
On trying to turn on the pc no sound at all,just the fan on the PSU and also on the Graphics card.Don't understand why it shut down on it's own in the first place while my son was extracting from winrar.

 

[Trialsfan]

Sorry for delay in replying Chobber but had to go out for a while.Can't say I noticed a light but will check and get back to you to-morrow as have things to do elsewhere at present.