When I plug it into my card reader it shows up on my computer for about 3 seconds then vanishes, it also wont work on my psp either.
I have a sony magic gate 8gig which I bought in Dubai last year.
What brand is the memory card?
Its a sony one
Can you test the card reader in a different computer? Maybe the card reader is the culprit of this 
Iv tried two card readers and two psp’s and one laptop
oops
It seems that the memory card is defective then
Perhaps you have a fake memory stick.
Please check this weblink. Scroll down the page and check if you can determine if you have a fake memory stick.