Genuine software is a term normally used for software that you have (or in some cases: haven't) bought legally. If you have a problem with some program complaining that something isn't genuine, then it is (or thinks that it is) an illegal copy.
If you tell us, what exactly the problem with your desktop is, we might be able to help you. If however your copy of Windows
isn't legal (which may or may not be your fault), the only legal way to solve this problem would be to get a legal copy of an operating system.
If you're looking for a free alternative to Windows, you could check out any Linux or free Unix distribution. We'd be happy to help you decide in our
Linux/Unix Forum, if that is the case.
Greetings,
Nepomuk