simo85 is correct. First check for a fuse.
Second, the A500 power supply is a switching power supply meaning if there is no load on it, it doesn't put anything out! Just turn on the power supply and check pins with nothing plugged in and you'll probably get no readings.
If you have a test bed/motherboard (don't we all?) you might plug the power supply into it and try getting readings at the plug on the motherboard.
Better yet, if you've got a motherboard that's bad, but you're keeping as a chip and parts source, plug it into that! As long as there's some sort of load on the power supply, you'll get voltages.
Good luck!
Curtis
