Here are a couple of quick checks to see what is going on.
Is the fan turning on the logic power supply?
Is the mother board seeking the floppy at boot? This means the MB is functioning and may be having other issues.
At one of the spare white plugs, do you have 5.05 VDC between red and black wires? Do you have 12VDC between yellow and black?
I do advise replacing a power supply this old.
Lastly, listen for beeps coming from the MB when you turn the machine on. The Bios may be trying to tell you something.