I have an emachines computer with vista...need to

If you notice your disk drive having a partition for recovery, you may have an option to do system recovery from boot up.

Most desktops have this option during the boot up process. So before windows logo appears on Startup, press F11 key.

This procedure will restore your computer's system from the very first time you used it. So, better back up all the important files and documents before doing this.