Hi there, My son bought a PSP memory stick, but when he puts it in the PSP it says "No memory stick inserted". He tried formatting it on the PSP , but gets the same message there.
The PSP and Sony have a magic gate protection system and certain sticks (ebay purchased ones generally) or cheap copies do not work. It is a copy system installed on the PSP/PS3 to stop use of unstable data etc. If the PSP can't find it, it means it is not official. Alot of copied cards look identical and you can't tell from looking at it. Go onto Sony's PS3 website and there are the instructions on how to test if it is genuine.