I had an A500 that started acting quirky on me once doing weird stuff like that and I bought a new bigfoot power supply for it because of an article I had read in an amiga mag suggesting replacing the weak power supply and all was well again. But you could have some other type of hardware issue, bad capacitors etc...
I also remember playing pal games on my A500 by using a boot disk that you popped in immediatly before the game disk, some of the pal games that I bought came with that disk. I think one of the boot disk programs was called relokick.
