Memory card.worked but doesnt anymore ???

I had used to use a legit 4GB memory stick pro duo magic gate mark 2 ( which was bought at best buy )

it was working grat for a while. Than i upgraded to a Sandusk memory produo 8GB.

But my problem is that my 4gb stick doesnt work anymore (but my 1 Gb which i had ealier than the 4 gb works)

Help