Just some tips:
Last series of A500 have the amber LED for floppy and green for power.
When you open your Amiga again, look for the circuit-printed label (near the expansion RAM header). There you will see the model of the motherboard.
It must says some like:
" B52/Rock Lobster (yeah, is the song from B52'S)
the initials from the crew who made the board
A500 REV. X.xx ( <- expect for 6 or 6A here)"
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For the rebooting issue: with the Amiga opened and not powered on, look for the keyboard header, see if it is properly connected and even further, if the cables are not loosing or peeled. If so, insulate them (one by one).
The keyboard "cpu" is in the keyboard board. If a problem arise in the unit, the capslock LED will blink a number of times.
If apparently everything is OK, close the Amiga case and go for the next, who is...
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The PSU
Whit it disconnected from the mains and from the Amiga itself, open the brick (four phillips screws). You'll not zapped or anything, just be sure to await half an hour after disconnected from the mains.
Check for bulking or leaking capacitors. If you spot one, swap it for an identical unit (the values are printed in the capacitor itself).
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Hope it helps!
