PC Help: Clock won't keep time

When I start my computer up, before anything is loaded and before Windows starts, a message comes up that says there is a “CMOS checksum error” and that the defaults have been loaded.

The only real problem is that the date and time is out: it always shows 1 January 2002. I can change this to the correct time and the computer starts up and runs fine, but once it has been shut down and left overnight, the problem reoccurs.
Colin Sutton

This is a fairly common problem in older computers: the battery has run out. The battery isn’t used to power the PC: it is used to keep the time and settings (such as what hard disks are connected to the computer) accurate while the computer is switched off.

Computer batteries are designed to last for several years but when they fail, the computer will lose all its settings each time it is switched off for a long period of time or unplugged from the power supply.

Modern computers can automatically adjust the settings from scratch quite easily, so the only problem most users will notice is that the time is out of sync.

It’s not difficult to replace the battery, but it involves opening the computer’s case and working with the components. If you’re not comfortable doing this, any local computer repair shop will be able to do the job for a small fee.

The battery is a flat, silver cell, which will be mounted in a battery compartment somewhere on the motherboard. You may have to move some cables out of the way in order to move or remove it – be careful not to unplug or dislodge any of them.

When you have removed the battery, make a note of the type, which will be marked on the top, and pick a new one up from a computer or watch repair shop. It shouldn’t cost more than a couple of pounds.