This Guide only provides a solution if you're having connection issues; in all other cases this Guide is of no use for you!

In my personal case the gameconsole wasn't showing any connection whatsoever, it was as if there was no internet. So if your computer does connect but then drops the connection, then the issue might be solved with one of the options fom the "I Already Tried This" list below. The final solution might not be of any help, but if you want to persevere you can always try.

For a lot of issues there already exist solutions on steamcommunity and/or youtube.
The solution in this guide may be your final go to if you could not resolve "Failed to Connect" problems with one or more of these (already known) solutions:

• checking game files integrity
  
• reinstalling the game
  
• resetting your router
  
• opening ports on your firewall
  
• disabling anti-virus and/or firewall
  
• specifying a custom port to connect (use +clientport and then a number between 27006 - 27032 as launch option (right click game in library -> properties -> 1st button on first tabpage); eg: +clientport 27007
  
• installing a new network card / using the other network interface in your computer (eg if you have both wifi and a cabled network)
  
• using 3rd party software of any kind that tinkers with your settings
  
• logging into windows with another profile / creating a new windows profile
  
• temporarily use you mobile internet (4G!) via Shared WiFi connection or USB (=tethering); disable/unplug your other internet connection
  
• unlisted solutions that still didn't help you (please reply to this guide if you have used a unlisted solution, i'll add it)

Tried these and still no result? Keep on reading, i've got a special one waiting...

This is how I got things working again; I've got a network here at home with all pc's having PRO versions of windows; this lets me set up VPN connections (receiving).
What i did was setting up a vpn connection here at my local natwork,and connecting to that vpn service with my gamepc (make sure you set up your IP manually for the network card your using with the vpn, otherwise all the internet traffic will still be routed through your own network card and the game probably still won't work); so you set up a local IP (eg 192.168.1.55) and the subnetmask (255.255.255.0); you leave the Gateway ip and the DNS IP's empty. Then you connect to the local vpn, normally this should be 192.168.1.180 if you have set it up in the same network (as it should be).
Now test quickly if your internet is working correctly (open the browser and surf to a website that has dynamic content like youtube and press refresh (F5)), if all is OK, start your steam and start CSGO.

Now the game should be able to connect to gameservers. You don't want to keep this situation offcourse; as you get a higher ping (an extra 1-5 ms on cabled lan, up 15 ms if on wifi) because of the VPN-loop you created. In my case, after playing just a single game, i deleted the VPN connection from my gamepc, and i set my previous network IP settings back (for most people DHCP/Automatic will be just perfect). After setting things back how they were the game ran perfect. so it's a glitch in the network stack of CSGO that needs to be fixed by overwriting it with new settings (vpn connection)..

Now, i hear lots of people already yelling at me; I don't have windows Vista/7/8/10 Professional (or ultimate for some versions); so i cannot set up my own vpn.
In those cases you have three options;

• Install a demoversion of windows 10 PRO (just install windows 10 without a key, i'll ask if you want pro or home; you can use it for 30 days
  
• Install Windows XP PRO on an old machine or a small partition (this takes much less resources than win10; you could settle for 5gb of diskspace and have plenty of space; only use this windows for the VPN option off course as it's not safe to use it as a gaming rig or workstation (don't even think about surfing the web!)
  
  
• Get a (free) account with a commercial VPN service, although i didn't really test this. You should look for a vpn service that works without installing extra software; windows supports most vpn types out of the box. You shouldn't invest money into this; i've take a quick look around and totalvpn supports the windows vpn client. if you want to use another one check if it has manual configuration options, then you're good.

When configuring VPN make sure you're using PPTP (point-to-point tunneling). It shouldn't be needed to configure the IP-options of the vpn-client side (the connecting side), the vpn-server side usually goes with 192.168.1.180 and will automatically give an IP that follows upon the given ip. You can also give an amount of available ip's, but be aware that with windows PRO you can only make 1 simultaneous VPN-connection to the windows PRO vpn-server. .
Also it's needed to create a local username and account on the vpn-server which you will use to login to, use accountmanagment to create a new LOCAL account + password. on the windows PRO that will act as vpn server; on the vpn client you don't need to create an account, you there just need to connect to the vpn server and give them those credentials (don't forget to select the user that's allowed to connect on the server-side).
To create a vpn connection, just google your windows version + create vpn connection (eg; windows 7 create vpn connection. because it differs quite a lot between certain versions and my guide is getting bible-sized already...

now, i hope you guys find this info interesting and even more helpful... I tried to give as much info as i could because i know how discouraging it can get when you want to play cs:go, nothing seems to work and valve is just not lending a hand to help you out. I even guess they wouldn't even come up with this solution as it is so far fetched. I know it was my last solution after having tried everything i found (which was suitable, because there is also quite some bad info around, like i found a video where someone puts his public ip adress behind the +clientport option) and like everything i could think of.
How i came up to this solution? I've been a repair specialist for many years for pc's and networks; that's why i try to think out of the box.

If you got questions, don't hesitate to ask!

Anyways, i'm going to conclude this 'biblical sized message' and hope many troubled players will find the way to any of the upper listed solutions or the explained VPN (temporary) workaround.

Happy Gaming!