When I insert my memory card in the ps2 it shows that "There is no data" but it still has at least 4mb of free space in it anybody know why? My memory card is a 8mb card and my ps2 is a Slim ps2

Just like SD cards or other media, they have a life span of how much read and write they will take before they burn out. If you hear a rattling inside something may have busted lose.

Start your PS2 without disc and go to browser choose the memory card and first time you see it's say there is no data...
The two or three time you see it and a few of saved files show up!and after that you see again that is say there is no data again...
Just repeat that until all the files show up!don't reseting your ps2!or it will restart from the first!