Doesn`t look too bad, like BoingBoss said, the -12V looks a little low.. but you`re testing the voltage without load so it`s only a ballpark figure..plus your voltmeter could be out of calibration..
But it shouldn`t stop the A500 booting as it`s only used for sound and serial port.
Are there any noises from the floppy when you power it up?
Does the power LED come on, or flash?
Have you done the tried and tested method of reseating all socketed chips on the motherboard?
