4-5 year old Gateway desktop PC will not boot

Hello,



This morning I came down to my PC with the Gateway logo staring at me.
64-bit OS, Windows 10 Home, version 1511, OS Build 10586.318 AMD A6 quad processor, 10 GB Ram.
It said something like Del: BIOS setup F12: boot options
But, pressing keys (Del or F12) did nothing.
I could press and hold the power/reset button to achieve poweroff.
I could press it again and arrive at the same dead screen.
In short, I had a very dead computer.

I brought out my laptop (even older) and browsed some.
I found a very old Ubuntu disk that my nephew had left for me years ago. I placed that into my CD/DVD drive and tried to reboot.

That created something different - I got a blue screen of death with a message about Critical Process Died. Then it went into reboot mode and Windows 10 booted. It shows my DVD drive has a Ubuntu Install disk loaded. I thought it was a 'boot from' disk. And since I know nothing about Linux, I had no idea what I was going to do if it did boot up in Linux!

In any case, it is (right this minute) working. But I have NO idea why it failed and NO idea why it worked. It failed many times prior to trying to boot with the Ubuntu disk loaded. Why on earth that would change anything is beyond me, since it is not a boot disk.

Anyway, I have read lots of google searches about my situation and they talk about removing batteries from the motherboard and rewiring the power/reset button (didn't know there was a difference). I am not a total novice, but not very experienced at this kind of troubleshooting. Any ideas?