Where is the CMOS battery on a Gateway ATX...

You can replace the CMOS battery yourself. Open the case to the computer and you will see a small round battery similiar to a watch battery. Its about the size of a quarter. Thats what you need to replace. email izzoaf@yahoo.com if any other questions.

Its on the motherboard.You can replace it.Power down remove power cable press the power button to drain the power.Open the case,the motherboard is a green circuit board with everything pluged into it.You are looking for a coin battery.Look carefully how its secured to the motherboard and slip it out.Now that you have it out RADIO SHACK USUALLY SELL THESE IF NOT LOCAL COMPUTER STORE.
GOOD LUCK

PC desktops are easyier than a laptop. it you lay on it's side and remove the screws the side will slide off and you will see the motherboard and on there will be a silver battery. just pop it out and replace with the same type. Google how to open up your computer if you cant work it out