I'll tell you what Commodore told our service guys when we a dodgy A500 came in for warranty, disconnect all cables, lift the A500 30cms in the air and drop it(preferably on carpet), worked then, worked for me when I pulled my A500 out the cupboard, and I'll bet it will work for you.
PS. Don't blame me if you kill it once and for all, I am only passing on an old trade secret.
BTW Welcome to a.org