i had the same problem with the av500, and i believe that i have both good news and bad news for you.
the good news is, you can get your device working again
the bad news is, youll have to deal with tech support, send the device in, and in the process of fixing it, they either clear the hard drive or get you a new one
believe me, i tried everything on my av500, and the only thing that worked was getteing aa new one, that archos supplied for free, which was good.(you will have to pay one way shipping though)