whatever you do
DON'T OPEN THE POWER SUPPLY
there won't be a fuse in there - the fuses are in the plugs .... same for the monitor (but I doubt it's that)
only an idiot would even think about suggesting opening one
see
http://www.sbprojects.com/projects/pcpsu/pcpsu .htm ....
what there will be is some huge capacitors that could just end all your problems
If the PSU is blown ... get a new on (they are cheaper than a coffin)
the other option is that it's your motherboard that's blown
the on off button is software driven .... if it's not working it could be.
power spikes can be very destructive
but I repeat ... if you do take it out (4 screws) -
DON'T OPEN THE POWER UNIT - there is nothing in there that won't kill you (unless you know exactly what you are doing)
if it's the power unit .... spend 30-40 on a new one ... the cheaper ones can't cope with mains spikes
(sound familiar?)