14.04 - UPDATE: Upgrade to 16 Failure + Google Chrome is not working anymore

I've been trying to upgrade my Ubutnu from 14.04 to 16.04, when I click on upgrading the system is shows me this error:

The required dependency 'apt (>= 1.0.1ubuntu2.13)' is not installed

I tried the sol here, but it didnt work with me:
14.04 --> 16.04 failed; apt (>= 1.0.1ubuntu2.13)' is not installed.

UPDATE:

I fixed the mentioned problem above, but still, I cannot upgrade to 16.04. Now is shows me this:

Error during update 

A problem occurred during the update. This is usually some sort of network problem, please check your network connection and retry. 

W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/stable/main/binary-amd64/Packages 404 Not Found [IP: 91.189.88.161 80] , W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/stable/main/binary-i386/Packages 404 Not Found [IP: 91.189.88.161 80] , E:Some index files failed to download. They have been ignored, or old ones used instead. 

Also, Google Chrome stopped working all of sudden. When I try to open it using the terminal, it shows me:

[8984:9017:0728/230608:ERROR:nss_util.cc(744)] Error initializing NSS with a persistent database (sql:/home/maldini/.pki/nssdb): libsoftokn3.so: cannot open shared object file: No such file or directory
[8984:9017:0728/230608:ERROR:nss_util.cc(212)] Error initializing NSS without a persistent database: NSS error code: -5925
[8984:9017:0728/230608:FATAL:nss_util.cc(214)] nss_error=-5925, os_error=0

Aborted (core dumped)

I removed and "purged" the program and then re-install again. I tried removing all the caches and config files. They all didn't work.

Any suggestions?