PC will not power up ?

[KJR]

A friend has an Advent T9306 PC which will not power up fully. When working, you switched on the PC and the fans would spin really fast for about 3 seconds, slow down to standard speed and the PC would then run through the usual start up sequence.

Now:

the fans continue to spin really fast,
the cd/dvd drives power up and you can open and close them,
the USB mouse and keyboard are not receiving any power,
the attached monitor is not receiving a signal,
pushing the PC on/off switch does nothing, the PC remains "powered" until you switch off the socket at the wall.

Any pointers as to what I need to look at to sort this ?