Q: I can't open terminal on Linux Mint I don't know exactly what happened, I am using this PC for a few weeks, I installed a bunch of packages yesterday and suddenly a lot of bugs started to appear.
After I boot the PC, select Linux Mint and put my password, the background disappears. The terminal can not be opened. Alt+F2 is not working. The terminal can not be opened by Ctrl+Alt+T, nor by clicking on any window and selecting "open in terminal". 
I can still enter on file explorer and click on files.  I can open Spyder, etc. I want to recover my system, but I don't know what to do, how to do. I don't know exactly what caused the issue, but I remember installing some packages, I also don't remember their names.
It is impossible even to turn off the computer.
I also recorded a video to show the problem: https://youtu.be/MpoYgYX_x_0

A: I would suggest to save to an external drive your stuff (given that you can open file manager) and reinstall the system. Even if you could remember what (packages) caused the issue, going back to the previous condition would likely brake it more. Anyway, not knowing what caused it makes it very hard to fix it.

A: The technical term for that is "your system got hosed". :-) 
Unfortunately, there are too many possibilities for people here to be able to figure out what the specific cause is. On the positive side, since you haven't used it for too long, you can start over without it being too traumatic.
If you have important files, back them up, then start from scratch.  But when you reinstall, there are a few things you can do to reduce the chances of this happening again, or make it easier to recover if it does.


*

*If you installed Mint in a single partition, use three partitions, instead.  Put root and home in separate partitions, and have a swap partition.  The swap partition will improve performance.  The separate root and home partitions will simplify backup, upgrading, and recovery from stuff like this.  This video, How to Upgrade or Reload Linux while Keeping Your Data, might be useful in understanding how to use a separate home partition to reinstall or upgrade without losing your data.

*Be organized and careful in installing packages.  Try to stick with what's in the repository because those packages will have been tested with the distro and possibly customized to work well with it.  You are generally safe using the Ubuntu LTS repository, as well, since Mint is based on Ubuntu LTS and already draws from there.  
Add packages from PPAs with caution; try to stick to ones that are widely recommended, and don't have reports of issues.  Ubiquitous packages like major browsers and office suites are usually pretty safe to install from the developer's web site, but you're taking risks installing something not mainstream.  Mint supports Snap and Flatpak applications.  Those are safe in terms of not messing up your system, but not all of the applications work flawlessly out-of-the box.  
The farther you venture from the repository, the more likely you are to encounter problems.
The first step after you install should be to run updates.  Then reboot.  If everything is working, set up Timeshift, which makes it easy to recover to a working system if things go sideways.  You will need a storage location for its backup files.  
Then start installing packages.  But don't just load a whole bunch of stuff that looks interesting.  Load what you know you need, and do it in increments.  Load one or two packages and verify that everything is working.  
If you want to evaluate packages that look interesting, wait to install it until you're ready to actually try it.  If you then decide you don't need it, uninstall it.  Besides recovering the disk space, it reduces the chance of problems.  As long as the package remains, so does its dependencies.  Some other package you want to install may have dependencies that conflict.
