Can't save to CMOS + CPU is unworkable or has been changed.

Hello, my motherboard is ABIT kx7-333.

I dont remember when did it start, but once when i turned my PC on, monitor or keyboard and other devices wouldn't react. I fixed this problem by clearing CMOS and restarting machine.

But since then everytime i boot my PC i get "CPU is unworkable or has been changed" message. I can just press F1 and continue working and everything works perfectly, except...

I noticed that if i go to BIOS and then try to save and exit (save to CMOS), computer restarts as usual, but i have same problem as back then - monitor, keyboard etc won't react, computer looks dead except hdd and fans.

Only way to fix this problem is to reset CMOS again, but this way i can never change ANY BIOS settings, because if i do so, i have to save it to CMOS, and if i save it to CMOS, machine wont start and i have to reset CMOS again.

At first i thought that there is some problem with battery, but i had other PC which was functioning perfectly, and both batteries were 3V so i switched them. This didnt fix the problem, what is more, it caused the same problem with my other pc!!! Maybe i did something wrong when changing batteries, or maybe battery was bad, but it used to work earlier, and if i change back to normal baterry it is still not working.

I flashed my BIOS to newest version, but it didn't fix the problem. I'm completely lost now, i have 2 PCs and i cant change any BIOS settings on them. And also i get 'CPU is unworkable or has been changed' error on both of them.

I don't think its hardware problem, because problem is identical on both PCs and hardware seems to work fine on both of them.

Sorry for my messy post, and thanks for your ideas!

Simas