Power Problem

I was wondering if some one could give me an idea on what is wrong with my computer. It happened after a power lose. The computer its self still comes on and sounds like it is loading, but my monitor just shows blackand goes in stand by mode. and the keyboard and mouse dont get any power(none of the lights come on) My system is windows xp pro. Some one told me it might be my power supply box ( ) They say it is simple to fix ( )

 

Since that problem looked so similar to mine, here is what I did. Exactly, trying to fix a computer for my daugther, shut mine off (I had to use the Internet conection) and when I plug mine back... puff!!! No power, power supply died on me!!! Tested with another one and Black screen, just the Xp logo, so thinking that my son's games played something, I started using another one and punish -my son and myself- without our main computer... First I could not access safe mode, after a couple of days I could and did a System Restore, after that runned cc cleaner, ad-Aware, MacAffee cleaner, updated the virus program and scanned, Norton System Works (this squeduled a chkdisk) and defragged with diskeeper, now is up and running, though I need some more RAM... Try something of this.

 

Being stuborn and hoping the computer fixed its self after a couple days of rest I started it up. What got on the screen was a thing saying "power supply something" and there was a count down thing that started from 5 and went down to one and then my monitor went on standby with a black screen. At the same time my lights came on my mouse and keyboard but as soon as the count down was over the little lights went out.