Do you use windows now, and if you, did you get it's intaller with the PC you had before?
No my pc came with window's vista then i got a friend to change it to window's 7, But not to worry, I can get my friend to place Window's 7 on it. (How can i install window's 7 if the pc wont run without any window's?)
A computer needs an Operating System to run any programs, depending on the hardware and the software with which you plan to use. In your case, you would want a Microsoft Windows Operating System. Windows 7 is the latest released version of Windows out there. To install it, you simply boot to the install CD that you get when you purchase the Operating System, and it runs the installer through the computer's built-in "operating system", so to speak. After installation, the computer then-on boots into the Windows Operating System and from there you can run your programs and games just as before.