|Presumably the battery is bad, incorrectly inserted or not making proper contact.|
That battery powers the memory circuit that saves the various hardware settings when the computer is powered down - if it's not working, most of the hardware will be redetected at startup (although the clock will be wrong). Any 'custom' settings will be lost.
You can still run like that, but it would be better to have it working
I'm not one of those who think Bill Gates is the devil. I simply suspect that if Microsoft ever met up with the devil, it wouldn't need an interpreter