E: Unable to locate package linux-generic-hwe-16.04 E: Couldn't find any package by glob 'linux-generic-hwe-16.04' E: Couldn't find any package by regex 'linux-generic-hwe-16.04'

Are you connected to the internet? Did you run sudo apt update?

Yes. I am connected to internet and I ran the update command before installing.

This is weird. Please edit your question and add output of cat /etc/apt/sources.list.

The easiest way is to do a fresh install of 16.04.3.

Well, this is not feasible- reinstalling Ubuntu 16.04.3

Is it feasible to post contents of /etc/apt/sources.list then?

I have already added them in details of the question.

I updated the question.

How to create create a default sources.list? How to delete /etc/apt/sources.list? And you after after that I'll be able to "add" repos. Please also tell exactly which steps to follow.

I added the command.

How to create create a default sources.list?

I wrote how to create it already. It can be done in GUI "Software & Updates"

Last question, how to enable all repos? I cannot find this option. Which tab, option exactly?

Check all options on the first tab.

Still not working.

Did you install the kernel?

Yes, I checked all the options from the first tab and then the command which you have given in the answer. The same problem.

Did the kernel install? Did you reboot after that? What does uname -a show?

uname -a shows: Linux HP 4.4.0-78-generic #99-Ubuntu SMP Thu Apr 27 15:29:09 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux. I tried to instal the kernel but there was some problem. Failed to download repository information. I tried many time but the same error came.

I have updated the kernel but the command sudo apt install linux-generic-hwe-16.04 is giving the same error and the bluetooth is not able to search for devices.

So you didn't update the kernel.