On a Linux Mint 19.1 PC (formerly, a HP Windows 7 PC, Intel Core i7), I was converting over to Linux Mint 21.3 OS with a downloaded ISO image. This image on a bootable DVD had been used to successfully install the same OS on two old similar HP Windows 7 PCs. The process started without a hitch. Then, this dufus panicked after he chose the option to uninstall, and then re-install 19.1. Having realized that the wrong selection had been chosen, I stupidly stopped the process in mid-stream. The disaster? I have a frozen PC, no 19.1, no 21.3. Here's the message on the screen: "error: unknown filesystem. Entering rescue mode...grub rescue>" followed by a blinking underscore. So, with the help of online resources, I thought a solution was at hand for restoration. Using the command "ls" there were a series of "files"?. Some were "not found," but one was unique with the Message: "Filesystem is ext2." Supposedly, this was where deliverance was to be found. These subsequent commands using the same "file" were used: "set root...," then "set prefix...," then "insmod normal." All was going well until the last command and then the response cancelled me out going forward with the directions. Here is the new error message with that last command: "error: file '/boot/grub/i386-pc/normal.mod' not found." Then, it was back to "grub rescue>" Oh, the agony of defeat. Remedies? Or, have I just destroyed a functional PC? Thanks.

Time to learn some other distros to start repairing the hard drive, and then, you should be able to do the installation the way you planned.

https://www.system-rescue.org/

You should have the option with that, if needed to do a wipe of the hard drive, an erase procedure. Or maybe I'm think of:

https://clonezilla.org/related-live-.../more_info.php

One of these has it. That would put, "No filesystem", on your PC, and then, Mint should be able to install just fine. If it's an SSD, just be careful not to do this same thing over and over and over, or the it might break your SSD. If you need further help, let me know, and I can help you through the process, by using a VM as my testing grounds. Don't worry if you don't know what a VM is. But I can give you generic instructions for the process if you need additional help.

Are/were the installs legacy or uefi? Do you know the difference? If not, do an online search to get the basics. It's going to be difficult to try to boot a system when you reinstalling over an older system and interrupted it. Did you try to install the new Mint to the same partition? Why not boot the DVD again and install the new Mint? What option to 'uninstall' did you see and where did you see that? Also, what wrong selection are you referring to?

You might have destroyed the installed operating system but you should be able to simple install from the DVD.

I would like to apologize for an initial "bad" performance in this forum. With my problem resolved, I was not forthcoming in sharing this officially with the site.
Dumb luck appeared to be in my corner. So, here's what happened. Awaiting definite directions for a fix, I decided to do an F10 on start up to do a system check in BIOS. This was both a hard disc test followed by one of the memory. Since both such tests had passed before the snafu, I wanted to see if this was still the case. Both tests passed again. On a lark, I then went to F9 to change my primary boot order again to the DVD ISO to see if perhaps I might not receive the error message, "grub rescue." And Viola, on start up the previously proven DVD ISO fired right up and now Linux loaded without problems.
A sincere thank you to the contributors. Your time and thought were much appreciated.
Scott