my wife's pc is now switching off and refusing to restart unless you turn the power off entirely or unplug.

initially i thought it might be overheating or have a faulty powersupply; i have changed the psu from the old 450 to a new 500w and it made no difference.

the agp graphics card has a 40mm fan that appeared to have a problem spinning up and i was looking to replace it, but it has a micro-2pin plug that no one in the UK can supply me! there's no extra 2 or 3pin sockets on the motherboard.

the cpu and case fans appear normal.

here's the strange thing, i am typing this message and so far the thing hasn't crashed... the difference is the side of the case is off. (this factor was why i originally thought of overheat psu).

any ideas?