What if motherboard battery is bad

If battery is bad, computer will usually ask for time and date to be set every time you unplug the computer for a while. Most motherboard batteries are coin type CR2032 and are 3Volt lithium even available at your local Dollar Store. They can be tricky to remove and replace, so if you have no experience with this, it is best to get professional help or just look for some tips on-line. The instructions for your machine can be seen here:

eMachines W3107 User Guide Page 58

I suggest you follow the instructions carefully before proceeding. If you need more information about the instructions, you can download the whole manual.