It depends on what the ms actually has written on it also... Psp's only run Memory Stick Duo's. So be weary of that.
Secondly, try alternating the way you try to read the memory sticks.
Maybe remove the MS, power on, insert the MS once it is booted and then see...
Or, start up your psp, go into usb mode, and check on your computer to see if you can see any files on ur psp.
It might also be worth while trying to format it, in the system menu of the psp.
You could try to use the memory sticks in another device in order to see whether or not they work. This solution would also tell you if your psp is broken...
As I said, try alternating the way you try to read the MS.... Things sometimes work because of the way you do them.