I placed my memory card in card reader and opened it, all the folder extensions got changed to .exe Could you please tell me how to change the .exe to folders back again and how can I restore them?

It sounds a lot like the SillyFDC virus to me.
Check out this link for info and removal instructions.

Good luck,
WallyH

It is virus Worm/Autoit.ANVE problem. Follow instruction here to save files and folders changed to .exe