Linux graphical shell and package manager removed

I downloaded the Synaptic program today, as I could not install the program due to problems with the package manager. The program showed that I have 13 packages that do not work and they need to be removed and updated. I agreed and after installing the updates, he gave an error that he could not remove a couple of packages. After that, the tray and the lower window with programs got there . The screen saver remained. After trying to update packages via apt-get requests, and getting no result, I went to reboot. Well, actually the terminal view opened. Folders are in place, everything is fine. After finding information on the Internet, I tried the command " install elementary-desktop. After the message that there is no such package, I tried to update the package manager and upgrade it. It didn't help, I looked at the source list and found the contents of this file on the Internet. (I decided to manually roll back the system in this way). I changed the file but it didn't help. When trying to update upgrade, the command writes. Failed to fetch (link to the specified repository) temporary failure resolving ppa.launchpad.net. Google gave out that you need the remove purge source file command, then fix and supposedly everything. It didn't help me. Made autoremove, removed a couple more packages. The fix and update also didn't help. Everything was done through a super user. If anyone knows what to do, please tell me. I would not like to reinstall the system. Thank you in advance.