First off, we need to start with a little more information in here. For example, what OS are you running? What kind of computer (and its specifications) do you have? How much free space do you have? what have you tried yourself (and succeeded or failed) when trying to solve this problem?
Also, did youtry setting up your OS all over again? It MAY be that the file explorer.exe has been corrupted and needs replacement. Try replacing it or setting up windows all over again to replace it?
Also, If you'r running Win95/98/Me, have you considered the glorious NT kingdome? (NT4/2k/XP)???