The solution is to replace your battery in your comp.
I jumped when I read the title to your post! Oh boy! I'm actually get to use my former skills as an embedded system developer again! I used to be a high tech engineer and switched to being a comp tech during the high tech collapse.
Anyhow, CMOS is a type of memory. It stores values/settings for your BIOS between sessions. When the BIOS starts up it reads them from CMOS and saves them when it shuts down (or whenever you explicitedly save settings within BIOS) Now, CMOS is volatile memory, meaning that it's contents will be lost in the absence of power. That's why your comp has a battery. The battery kicks in when you turn off the power to the comp and recharges when you power on. But over time, batteries can lose their capacity, hence, your CMOS loses it's contents between sessions. The BIOS can only check the checksum of the CMOS contents to determine if something is wrong with the CMOS but exactly what caused the checksum failure, it can't tell. What tipped me off was that everything returns to default which means all the CMOS data was lost. That usually means the battery is dead.