Strange PC behaviour...

[Geezer57]

I'll be very grateful if you could explain it a bit more.
It is happening repeatedly. I get a message 'CMOS checksum bad. Date and Time not set.' Then I have the choice to run BIOS and set it or load the default values. I first thought there was something amiss with the system clock in the PSU itself (that oscillating crystal or whatever it's supposed to be), but I'm sure your diagnosis is better.
I'll get the battery checked, but err.....what exactly do you mean when you say 'check to ensure that you don't have the jumper set to clear BIOS.' ?

I'm concerned about an erroneusly-written BIOS. I wonder if updating your BIOS would help. Nothing sure here. Consider this as a loud thinking baloon.

As long as your machine is running O.K. after you restore the BIOS settings, I wouldn't think you had a bad BIOS flash - those usually screw everything up and the computer won't boot at all. <ask me how I know>

Sounds very much like a motherboard battery gone dead - your symptoms match perfectly. Not expensive or difficult to replace, and can be done by novices, but it would help if you had someone familiar with the work to help.

As far as the jumper set to clear the BIOS, that's pretty straightforward. Almost all motherboards have a 3-pin header on them, with two of the pins covered by a shunt cap (plastic thingy). Normal operation has the cap usually on pins 1 & 2 of the header, with the cap on pins 2 & 3 the BIOS is shorted out (clears it) and the machine won't run. If you haven't been messing around inside, that's probably not the problem, O.K.?