Black screen - No boot up possible

Hello,
Dimension 5000 series, desktop worked fine, then left it for 1 hour. When I got back initially I thought it had gone into standby / hibernation mode (I was wrong !) with a black screen and the power button flashing amber.
Now I can not power up at all !!
I press the power button and nothing, I know theres power in the PC, as the internal motherboard LED's are on, the key board num lock LED does not light up at all. My PC is set to auto windows update, I cant confirm if it did indeed have an update.
Note: I cant boot up at all, therefore cant open the CD tray, can't enter BIOS or safe mode, I cant do anything.

Writing this note on a mates laptop.

Any one experiencing this issue ???

Thx.