CMOS Checksum Error, and having to set the Date/Time repeatedly, generally points to a bad CMOS battery.
If it were I, I would replace the battery with a new one. However this is what I would do.
Your computer is still under warranty. Opening the computer case may void the warranty.
Therefore you may not come to the same decision that I would.
On the motherboard is a round flat battery about the size of a U.S. Nickle.
It's a type of watch battery. Generally a CR2032.
A CMOS battery will generally last from 4 to 7 years. Perhaps the CMOS battery installed in your Gateway is bad. Just a lemon that came from the battery factory.
The battery holder on the motherboard is rounded in shape to fit the battery, and has a metal clip inside. There are different styles of fastening used in the clip design, but generally a small tab of the clip is eased to the outside edge of the battery holder, thereby releasing the battery.
This article will 'shed more light' on the various styles of CMOS battery holders,http://www.hardwaresecrets.com/article/81
Proper procedure in order to replace the CMOS battery;
1) Unplug the computer from power.
[NOTE* Always unplug the power cord from the surge protector, and not from the computer's Power Supply. (Back of the computer) Unplugging from the Power Supply MAY cause a voltage spike. ]
2) Observe Anti-Static Precautions
Your body carries Static electricity.
Static will fry out (Short Circuit) the delicate hardware components inside a computer.
ALWAYS relieve your body of Static BEFORE working on a computer.
Computer unplugged from power, computer case open, TOUCH the metal frame of the open computer case.
This action will relieve your body of Static.
Should you leave your computer in the middle of working on it, be SURE to Touch the metal frame again upon your return.
3) Opening the computer case:
This is Gateway Support, and the Support Documents page for the Gateway DX4840 series of Desktop Computers,http://support.gateway.com/us/en/s/desktop/2010/gateway/dx/dx4840/DX4840nv.shtml
I would like you to click on - Product Views.
Now click on Rear View.
Observing the rear of the computer look at the right side. Along the edge down towards the bottom is a screw. This screw is removed, then the Side Panel is pulled towards the rear of the computer.
(There is a raised portion, or hump, in the Side Panel for placing your fingers)
If your Gateway DX4840-11e desktop computer has an Asus M2N32-SLI Deluxe motherboard, the CMOS battery is located down towards the bottom of the motherboard, and slightly to the right.
For additional questions, or clarification to what I have stated, please post in a Comment.