I have been running LM 17.3 Cinnamon, updated from 17.1 with kernel 3.13.0-37 on my ASUS computer with AMD A10-7800 with Radeon R7. After much tweaking of the system, I finally had it running well - until this morning. Yesterday, the LM Update Manager told me there were a number of software updates available and I installed them all. I think one of the updates may have been for the AMD video drivers, but I'm not sure. Nothing noticeable happened immediately after the updates and I worked with the computer until I shut it down for the night. This morning, when I tried to reboot, it told me that Cinnamon had crashed and I was in Fallback Mode. I tried to change something - can't even remember just what - and reboot, and now it won't even go into Fallback mode. Just a black screen after the grub menu. I do have Timeshift installed, and have even used it successfully some time ago to revert to a previous system configuration, so rolling the system back to a configuration before yesterday's updates would likely solve the problem. But I can't access Timeshift because I can't get into Mint at all any more.
Any suggestions would be gratefully received.
Thank you.

Say what !!!
How can you not know what you did ?. Better start taking notes - maybe then we can help.Good. Knowing a backup system works is gold.
I see mention of restoring from liveCD/USB, but didn't find an example. So boot your Mint live medium, add the ppa and install timeshift. Then do your restore using the backup directory on disk - presuming it is still valid.

This does not solve your problem, and for that I apologise.

However, for / backups, I use Macrium Reflect installed on a YUMI-created USB key to backup my root partition (my home and other partitions are backed up in more conventional manners).

It takes 5 minutes to boot off my USB key and backup the root partition to an external HDD, which I do on a regular basis or before important system configurations. That means that if my root partition goes up the swanny, it takes me 5 minutes to reboot off my USB key and restore it, rather than having to immerse myself in a failed system in order to restore the partition.

Of course this is only useful if you're not running a server or any other configuration that makes system downtime a problem.

There are probably other more Linuxy ways to do it, but boy does it work well.

Thnak you, syg00 and hydrurga, for your suggestions. I didn't follow either of your suggestions exactly, but yours, syg00, inspired me to try something else, and I now have my system back. I realized that I did have access to a linux command line by selecting recovery mode at the grub and then selecting root. My problem was that I really don't know how to use the command line at all - I'm a Linux newby and haven't learned the commands yet; I've only the terminal in the past by cutting and pasting commands from instructions I have found on sites like this one, without really understanding them. But by googling around and a great deal of trial and error, I was finally able to run Timeshift successfully from the command line and restore to a point a couple of days ago, before the updates that I thought had probably caused the problem. And voila! Everything seems to be running as it is supposed to now. I'm a happy man again!

Excellent.

If you can remember the steps that you took on the command line to resolve the situation, please list them here for others with the same problem.

It's always a good idea to keep a track of the steps you take to resolve problems.

FWIW I won't consider a backup system that doesn't have a simple (documented) CLI.
Especially if it has a rsync back-end anyway.

I suggested the liveCD as it was a simple means of getting to the GUI without affecting your installed system. Glad you got it sorted.

Thanks again to both of you for your respective suggestions. As suggested by hydrurga, after much trial and error, here is the essence of what I did. The following assumes a situation such as I faced: Timeshift was installed in Linux Mint and had been automatically creating backups, but I couldn't boot into the Linux Mint home screen because of a graphics driver problem which caused a completely blank black screen immediately after selecting Linux Mint from the Grub menu.

From the Grub, select the choice to boot into the Linux Mint recovery mode. At the recovery mode menu, select "root," and then, when asked, enter your LM password. Then, into the command line enter "timeshift --restore" (without the quotation marks). You are then asked to select a number of things. You are only given 3 or 4 seconds to make each selection and if you don't make the selection in time, the command aborts and you have to start over by re-entering "timeshift --restore".
In fact, I had another problem to overcome: the first time I entered "timeshift --restore, I got a lot of error messages about various folders being "read only". After a google search, I followed one suggestion, which was to enter "mount -o remount /".

WARNING: The same "askubuntu" page that contained that suggestion for overcoming these "read-only" error messages contained input from others saying that this was a dangerous command because it caused the system to bypass protective safeguards. But it worked for me, seemingly without ill effects.

I had to start the "timeshift --restore" command a number of times before I made it all the way through the choices before timing out and causing the command to abort. You have to identify which partition your Linux Mint system is in, which of the Timeshift backups you want to rollback to, whether you want to alter the grub (-I didn't-) and a couple of other things. Once you get through all the questions successfully, the system rollback starts and can take a few minutes (with lots of filenames scrolling across the screen.) When it's done, you will get an instruction to reboot. When I gave the reboot command, it actually put me back into the recovery mode menu, and I selected the "resume normal boot" choice, which took me back to the Grub menu. Then I selected the default "Linux Mint" choice and this time, instead of the black screen of death, it gave me the LM logo and booted correctly. Been running fine ever since.

As I understand it, Linux Mint and Ubuntu are pretty well identical at the command line level, so I'm pretty sure that the above would work

One last comment. After you first get to the command line from the restore mode menu and have selected "root" and entered your password, you can enter "timeshift -h" or "timeshift --help," which will show you pretty well everything I have described above, and will also show you alternative ways to do the restore. So, in response to syg00's comment that he won't consider a backup system that doesn't have a simple documented CLI (command line interface). Timeshift does, in fact, have a simple documented CLI. That's how I figured out how to do this. I was just very inexperienced with the CLI and so was unnecessarily afraid to try using it.

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Excellent description of the steps involved. Thanks mgerson!