I have a PSP 2001 which was previously either 4.01 M33 or 4.05 (cant remember) that captured a virus, so I had formatted the memstick, and tried to upload some .cso games that I downloaded, but the games were not detected by PSP. I read I have to upgrade, then downgrade to lower versions to get the games running. So I then went to upgrade it to 5.01 using ChickHens hack method through online instructions and was hoping to get it downgraded after that, but seems I am stuck. I also found out that versions 3.++ up (?) also could not boot using Power+R button, which I figured essential for one to get the .cso files up and running. I am not sure if this is inferior only to PSP 2000 or lower. Now I`m at a loss since it says the Game is Corrupted, and now I`d like to revert back to the old 4.++ version. Or, if anyone could give me instructions/confirm if PSP 2001 can be downgraded. Anyone?