This problem is actually with my friends computer....well my friend called me and informed me that his computer wouldnt turn on and that the PSU light on the back of the computer was flashing. I told him that his PSU was probably dead. So today I did a search for a flashing PSU light on google and I actually got an article from the HP site. We did all the steps from pushing in the power button for 5 seconds and reseting the button on the PSU. For some reason the power connectors are extremely hard to remove from the drives, but we finally removed one from the optical drive and the light was still flashing, then we took off the big power connector of the motherboard, this time when we plugged in the power cord to the PSU the light just stayed off, no flashing. Then we started taking off all the fan connectors that plug into the motherboard and even took off the 56k modem but we let the big power cable that goes to the motherboard(im sorry I forgot what its called) and the light was still flashing. Ok so heres where Im stumped, Im quick to assume that the motherboard is at fault but Im not 100% sure becuase I didnt remove the power from the 2nd opitcal drive,hdd, floppy, and obviously I didnt remove the cpu. So it can still be any of those things. But how come when I disconnected the big power cable that goes to the motherboard the light just stayed off, instead of flashing or just solid. What do you guys think? Thanks in advanced.

The motherboard controls the power supply. It checks all the voltages put out by the power supply. If they are all within specs it sends a 'power good' signal to the power supply allowing it to stay up. If the power supply does not get the power good signal it shuts down.

Do yourself a favor BACKUP!

So what do you think maybe causing the problem then? so your saying that its not the motherboard?

Were you toying with it with the power plugged in?

It's not mine its my friends, and he mentioned something that he disconnected it because he was going to move it? any ideas what it can be? I guess our next option is to disconnect every single drive and fan, and if the light is on then its a hardware problem, but if it says off then its the PSU according to the HP website.

My friend has just rang me with exactly the same problem. She got on a twitchy one about leaving things plugged into the electric cause she was out overnight, she has just returned home turned on her computer and nothing....just the flashing light at the back near the power supple.
I've just got her to go through some of the steps on the HP site but to no avail....bit strange it happening the same way for both of them :)