How can I fix a power supply, FSP Gprup, 250W, 2001?

How can I fix a power supply, FSP Gprup, 250W, Make is Medion 2.8gig 2001 The computer will not start at all except for the processor fan. It has an led button start. It used to start once the button was touched once. Then It would sometimes require several attempts during which it would tick tick tick as though trying to start a relay but failing. Now, it just won't start. The fan stays on so the back power switch must be used to cut all power. If it is a power supply relay, is it possible to modify it say with another added switch? Or, replace the relay, or discover where the power is not getting through?