Even if your PSP could see the memory stick, it seems to show it's capacity incorrectly.
Originally Posted by spud42
That is not a good sign.
Does your memory stick activity LED blink at a regular interval after the PSP can't see the memory stick?
That's a case of the memory stick's gold fingers having poor contact with the PSP's memory stick slot.
Of course, memory sticks do go bad... and the PSP's memory sticks seem to go bad really easily at times.
I had a friend with a situation like yours, but his was a much older 2GB Sony MemStick Pro Duo.
That stick was occasionally becoming "corrupted" on the PSP, and formatting it with the PC helped for a few occasions.
But later on the stick packed up for good (The PSP either says that no stick was inserted, or formatting would fail if the stick was detected). :X
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS