PC locking up.

My PC in my VMC is back at it again.  It will lock up while Linuxcnc is running.  I thought I had it narrowed down to a bad USB drive that I left in the USB port on the control panel last year.  It ran for about another year before having another episode.  (which that time it ran a 1/2 EM across the part 3/4" deep)

When I was working on the tool changer it did it to me a couple times.  Changed the keyboard, mouse.  Did not do it for a while, I just happen to be using the Vista pendant and it did it again ( I thought it was the pendant that time) So I have been running without the pendant. 
Tonight I needed to do a small tweak to a program so I stopped the machine, went to the mouse to open the NGC and make me depth change and it locked up on me there.  I do not have enough USB ports on this machine so there is a USB hub for the Keyboard and mouse, Touch screen is plugged directly in, and the pendant and remote USB port on the panel is plugged into another one.  All the cables run from the PC in the control cabinet to the front of the machine underneath it and are protected and undisturbed.  This is a Dell Optiplex that is probably pushing 15 years old, I have a fear that the power supply or the motherboard is trying to die.

Does anyone have any troubleshooting advice on this ? I am half tempted to just suck it up and get a new machine, I just can't make a decision on what to get.  ( I am running Pico PPMC ) I would like to figure out if there is a watchdog that I need to enable to stop motion if a loss of PC control happens during a run.  I got lucky on the time it did it when it buried the endmill and I was only a couple steps away. 

Recently I installed Mint 20 / LinuxCNC 2.8 and had a devil of a job trying to prevent it freezing randomly. Finally, at tommylight's suggestion, I changed the kernel to 5.10 which has completely fixed the issue. My machine has run continuously for more than 10 weeks now without issue.

Your problem sounds as if it may be different due to the maturity of your system but if you DID upgrade and reinstall, you'd be mighty frustrated to encounter the issues I did! Perhaps you will keep this at the back of your mind just in case:
forum.linuxcnc.org/38-general-linuxcnc-q...ezing-solved?start=0

I'll check that thread out, actually I hadn't done any updates in years. I did recently update the software, but had this occur before the update.

Thanks!