I have an e machines desktop with vista. My cd rom will not run any cd that I put into it. It will not even show up in my computer. Is there something that I can do or is the cd rom just bad?

Follow method 2 on this link, if this does not resolve problem, the changes you may have made will not effect your computer operation in any way - even if you do not get error 31 follow these steps
You can no longer access the CD drive or the DVD drive, or you receive an error message after you remove a CD recording program or a DVD recording program in Windows XP: "error code 31" (http://support.microsoft.com/kb/314060)