Big time problem

Some back ground- I am 68 years old, have a couple college degrees, so I don't think I am intellectually challenged. Perhaps I am though, will reserve my opinion on that.
I use the computer primarily for inteet searches for information, for word processing and processing and sending pictures to be printed.
I switched to Ubuntu because i had hoped to find something less onerous than windows and Mac with their constant changing of photo programs. I recently installed Mint on THREE computers and used it successfully for several weeks. Within the last week, when I try to install a program, the program MINTINSTALL (sp?) kicks in, and asks for a password. I have tried every password ever associated with any of the computers to no avail. I don't store anything on the computers that isn't backed up, so that when I get bolloxed up, I can just reinstall my OS, but I can't even do that now, on any of the computers.
I tried removing one of the hard drives and formatting it on another computer, but can't do that because it asks me for the root password, and apparently only Merle Haggard's ghost knows that.
By the way, I never installed a password when installing Mint, but using "password" doesn't work.
What is someone in my position to do? Use a computer until it bonkers up, then throw it away and go buy another? That gets kind of expensive. But I would like to spend more time writing and working photos than I do writing code in terminal that don't fix the problem.

Thanks for any advice
Fred