You can do that with MX 17; install it to a USB or run live with persistence enabled, meaning any changes you do will persist across reboots like installed packages and customizations. It's quite easy, just boot up your Live MX 17 USB stick and follow the instructions on this video
It takes no more than 10 mins or so and with it you could access your drive, rescue your data, download MX 19.1 again ... you might even use it that way if it works fine for you. I've got a laptop few months ago as a payment for a job, it has no hdd and I've been playing with some distros running from USB, either installed or with persistence, one of those is antiX, which is the base for MX and they both share that feature among many others, that's why I'm suggesting you to do that; it's easy, it works and it's quite an interesting learning experience. Once you've rescued your data and done anything else, you can proceed to reinstall MX on your drive. Also, it might be a good idea to keep that live-persistence MX 17 USB around, just in case you needed or simply just, you know, because you can
Thanks for the video link which I shall watch shortly.
I'm not sure which Live mode I have MX 17 in, but wherever the options are, as I'm sure I've seen them at some point, I'll retain or switch to "Persistence" mode.
Although I first used Linux (on a small scale) in 2016, it's only since March that I've become a regular user, initially only on my Desktop, but eventually also my laptop (as I haven't yet had chance to convert Windows 7 to MX Linux on the laptop due to being very busy, but will do asap once I've gone through the rest of the files including photos and backed them up to USB sticks, so I'll add extra sticks to the ones I referred to in response to Captain Sensible, so that I'm not short of sticks), so Linux is very much a learning curve to me, but invaluable means of computing, which I'll eventually be able to do second nature, but at present, besides my ongoing desktop hardware error faults, I'm learning how everything works including from you, Captain Sensible and Wizard From Oz among other members.
I suspect that my desktop hardware will have to be repaired or replaced once the Lockdown ends (as all computer engineers are in limbo due to the Corona virus pandemic), but until then, if there are any ways of reducing the number of errors in my hardware (depending on if this can be done, and what's causing the errors), this will increase my scope of using my desktop with less distractions.
Most importantly of all, regaining access to my hard drive and determining the source/solution of the puzzling outdated MX 19.1 download with GRUB errors appearing on unrelated USB sticks are my top priority, although anything that helps me in the right direction in any/all three of my topics will move me forward towards my goals of maximum possible usage of my desktop. I will also use my Laptop (whose hardware is not faulty), but I mainly use my Desktop.
As you're recommending me to try out AntiX, I'll also do that, as I'm more than happy to take up any relevant suggestions you, Wizard, Captain, anyone recommends to me. I'll work my way through your/their/other members' suggestions asap as and when time permits during the weekend and beyond.
To accommodate the above, I'll buy more USB sticks than I'd originally intended, which will be a good thing, as I'll have more sticks to hand for increased flexibility of different programs per stick.
Among my USB sticks, I'll use a brand new one for a further attempt to install MX 19.1 (a future new May ISO image download) onto a stick, once Wizard posts what I think will be some means of eliminating whatever is causing the February download with GRUB errors from ever appearing again, as the 1 May download should have gone to the stick (different from the February one).
Another option that comes to mind is that, as my Laptop's hardware isn't faulty, I could place my MX 17 USB stick (free from GRUB errors) which I'm using to reply to you into the Laptop, download MX 19.1 from Sourceforge (instead of the MX Mirror page - London, UK option I chose before) onto a brand new USB stick.
If this option works, being a different computer, it won't have any old traces of the February downloaded with GRUB errors, and being a brand new stick, its first use will be on the Laptop, thus no GRUB errors.
If all goes well, I could then return the MX 17 USB stick I'm using now back to This computer, together with a hopefully correctly installed MX 19.1
new USB stick (created on the Laptop) which will then lead me to click on "Install" to overwrite MX 17 with MX 19.1 on this hard drive.
How long my computer runs without shutting down or restarting automatically in the middle of the process could impact or not the outcome, but at least the USB stick would be intact so I could simply re-insert the stick.
It's all hope, but a likelihood one of the above options will get the MX 19.1 issue resolved.
If this does work, I'll keep MX 17 to hand, just in case anything drastic goes wrong again, but all going well, I'll have MX 19.1 (without GRUB errors) up and running very soon.
