I recently bought a working Sony memory card. I've been used it several times on both my PSP and my Sony camera, and I'm sure it works fine, so it's not a physical problem.
I ended up putting a virus/corrupted save file for a game in my PSP. Upon doing it, my memory card instantly went empty, stopped being recognized by the PSP and by the PC as well.
Being so, I can't format, I can't scan virus it, I can't acess it whatsoever. When I insert it in the USB slot in my PC, it lists as 0 Kb / 0 KB of available space. Could not format it through cmds either (I'm on a windows 7 64 bit).
Would greatly appreciate any help. Afraid the memory stick is completly dead, but hoping it's not
Download and burn a cd copy of UBUNTU linux. you should be able to boot from this cd. See if Ubuntu can recognize the memory card, and format it. if this is successful, you should be able to boot back to windows and reformat the card.