If you can remove the Memory Stick try plugging into a P.C. if you have a Card Reader. If P.C. recognises it but says that it needs to format the card. It is typical case of corrupted Zero sector. Run a checkdisk on it through the Command Prompt.
If not sure how to do one, follow these quick steps.
Press Windows Key and "R" together.
type "cmd" and press enter.
Make sure you know disk letter, example P: drive.
type the following.
chkdsk p: /f/r
Press enter and agree to whatever it prompts you with. If will perform 5 passes over disk (Memory Stick) and repair any errors. Once finished it will display whether or not it found any errors.
Plug back into PSP and see what happens. It should work again.
Hopefully P.C. does not say the Format thing and you can access all files. If this is the case then you have damaged the internals of your device.