When I press the power button, the lights come on

Is there a quick blue screen that says (at bottom) something like "cmos = checksum fail"?

the cmos is a (10 yr.life) button-cell battery located on the motherboard (under keyboard) and needed for the computer boot.
To replace great care must be taken not to break the plastic battery holder ( drys-out with age, try a small amount of oil on a cotton-bud ) and not to break the solder ,
hold down the bettery holder as you lever out the battery taking time to ensure there is no damage.