Can not boot up my computer i cant find my windows

You can call Gateway and order a replacement CD for $30 or so. If you have a friend with an Operating System disk, borrow it. As computer turns on, press key to enter BIOS (usually F2) and find where it says "Boot Order". Set the CD drive to boot first. restart the computer, Press any key when prompted. Use the COA label on your computer for a serial number. Being a Gateway, you will need an OEM disk for this, but can be any OEM. You will have to change the product key on activation. Do not tell Microsoft you used a different CD, or they will blacklist you. Once the activation is complete, your COA should work fine.