computer power supply ?

[nota]

my power supply is not coming on
typing this from a very old mac power book

my Q6600's power supply is not turning on
it is a rosewill RP550-2

the computer was not outputting a video signal at start up sometimes
multi restarts were needed to get it to have a signal
and the front power button was not working [needed to use the rear switch on the P/S]
yesterday it refused to do anything no lite no fans ect

does the power supply need a input from the M/B to turn on ?
does the front power button make a contact [can it shorted]
any way to test the P/S or get it to turn on if not hooked up to the M/B or front start button