How to restore android (6.0.1) on Nexus 5 after a failed shutdown?

Question

Android

On a small charge, the Nexus turned off and apparently something was saved with an error.
Symptoms:
1 - home buttons (circle) and recent applications (square) do not work, but the return works (triangle)
2 - I can not lower the curtain (two swipes down), but I go to the notification panel (one swipe). I can only enter the settings (gear) through the application panel
3 - the applications themselves and accounts are in working order
4 - before the problem there was a notification about a problem in the System
What could be the real problem and how can I restore the system without losing data.
PS: The smartphone is not rooted.

Answer 1

1. Connect via adb to your computer.
2. Make a backup of the data.
3. Put the recovery.
4. Make a data wipe.
5. Roll ROM with the system.
6. Restore data.
An abundance of information on the topic can be found on w3bsit3-dns.com, search the forum for your model and the corresponding flashing topic, you will also find the ROM archives you need. I reflashed my Samsung Galaxy Note 3 to the firmware mod from SGN7, for the first time I messed with the software and turned it into a "brick", after a few hours of googling I was able to safely "revive" and interrogate without outside help from specialists. It's been running like clockwork for a year now and no complaints. Then I restored the firmware on the girl's LG G2, also according to the w3bsit3-dns.com manuals and also successfully. Go ahead, the main thing is to follow the instructions in the manuals and not be afraid if something goes wrong.