Need geek help

My Dell PC is 3 1/2 years old - Windows 10, 64 bit.

My internet connect is wireless, and my computer does not recognize the 5g signal, so I'm connected wirelessly via 2g. Not really a problem, since speeds are 50x5. However. . . I'm paying for 100x10 thanks to an upgrade earlier this year that I only learned about yesterday. (I thought the small price increase was just that - a price increase. But it was for the higher base speed.)

Here's the problem. When I plugged in the ethernet cable from the router - so that I could get the 100x10 speed - all hell broke loose. Basically, the computer froze with vertical green, blue, red lines on the monitor. Reboot was unsuccessful, and Windows 10 doesn't seem to recognize F8 during the reboot for safe mode. Eventually, I decided to remove the ethernet cable. It took a few tries, but it booted up. I then did some cleanup - updating drivers, disabling apps at startup, and the like.

It's working fine now, though I'm terrified that I'll run into problems at the next reboot, but that's for another time.

I searched and found that others have had the ethernet cable/no reboot issue. From 2010 and 2015. In both cases the solution involved BIOS changes, and I'm hesitant to do that. And, unable to get into the BIOS in windows 10, I'm not sure this would be easy in any case.

So. . . any similar problems out there? Solutions?

And, yes, a new computer is likely within the next six months, so this will eventually be a non-issue. But it's an issue now. So, help!