Why is my comp clock off by 4 years?

I woke up this morning and my computer clock setting is off by about 4 years (date and time).
I reset it but what would cause this?

 

My desktop PC has been off by an hour or so at times, but nothing of that magnitude. Could very well be the CMOS battery, Rob.

 

I also would suspect a failing CMOS battery. I would replace the battery. They typically are a CR2032 wafer battery commonly found at any watch/battery/camera counter. Just make sure you unplug the computer from the wall and touch bare metal of the case interior to discharge any static in your body BEFORE reaching in. Do not touch the new battery with your bare fingers as skin oils promote corrosion and attract dust. I put a clean sock over my hand.

Make sure the case interior is clean of heat trapping dust while in there. Connect power and boot directly into the BIOS Setup Menu. Reset the date and time, make sure your drive boot order is correct (likely is unless you changed it in the past) then "Save and Exit" to boot normally. Hopefully you will be good to go.

While these batteries are supposed to last many years, I have seen them fail prematurely. In fact, I just had a CR2032 in my bicycle sensor fail after 1 month!

 

The company I used to work for fabricated brass and copper sieve cloth, and we had to wear white knit gloves (T-shirt material) to protect the cloth from skin oil contamination. Never thought about using a sock though. Good advice, Bill.

 

I used to have some of these when I was in the military for "white glove inspections". Those would work fine here too, if clean. Clean is the key word there.

 

Thanks guys for all the helpful info.

I replaced the CMOS battery even tho the old one was only 2 yrs old and still tested "Good".
I had cleaned the insides several months ago so I don't think heat buildup was a problem.

It's still a mystery but everything seems to be working ok for now.
I'll settle for Steve's comment above that it could have been a "fluke" as the best guess at cause.

 

How did you test it? Understand all batteries must be tested while the battery is under a load to be a valid test. Just sticking multimeter probes on the battery is not a good test.

 

Bill,

I tested the battery with an old Micronta 22-032A / Radio Shack mult-battery tester which I believe does check all batteries under load.