psp pandora help

can anyone please help
iv recently just bought 2 psp slim's using the how to tell if your psp is hackable without opening box trick.
both were firmware 3.90 and both had f on the box
the problem is pandoras battery works faultless on the white psp but when i try it on the silver one all that happens is the psp goes into the recovery menu and not onto the install custom firmware option,can anyone please help it is driving me up the wall and im just going round in circle
thanks in advance

iv sorted it now thanks for looking,the bloody right shoulder button was sticking so it was going into recovery instead of custom firmware menu
cheers