Samsung gravity PNY 4gb memory card problem

I've purchased a PNY 4gb memory card is a regular HC memory card and when i put it into my phone it asks to format the card so i do it on the phone and then it gives me the folders music, pictures,etc. Then i take it out of the phone and put it on my computer to download music and picture but when i do that an error message comes up and says not enough space on destination file. and when i check the size of the card it says 48kb I try formatting it from the computer when i do that it formats it and then i double check the size again and then the size is 4gb i load my music and my pictures and then when i put it on the phone and try accessing the files it only gives me the option to format the memory card again. I do not understand why is not accepting it. If you could help me that will be great thanks.