Sometimes I shoot tin the dark and hit something.
Here is a shoot in the dark. You might have a
failing crystal.To test the crystal is hard to do with ordinary equipment. It is easier to replace the crystal.
Quartz crystalIt is used wherer ever exact timing is needed. You will have to consult you documentation to find which crystal your mobo uses. I can not even guess.
There are three different timing things.
The CPU click
Time of day and system timer.
Graphics display timing.
A system might have up to three separate crystals. Or maybe four. Some sound cards have their own crystal.