Do you mean you cannot remote desktop into other machines? Or that you cannot remote desktop into your Windows 8 computer? If the later, that's probably because you don't have the Pro version. You can still do Remote Assistance, but you will have to use something like TeamViewer otherwise.
Did you mean you don't have like a program for remote desktop or that you have it but it does not work.
If its not working, do you use it for a windows 7 computer or from a windows 7 computer. Because connecting to or from remote desktop on a windows 8 computer only works from or to an other windows 8 computer.