When you get disconnected in a game, does your internet connection disconnect for a brief moment or is it just in CSS ?

I would try disabling your firewall and running CSS as administrator if you're using windows (right click, run as administrator. even if your acc is admin, running a program as an administrator will bypass some verifications that windows automatically runs for programs that use the internet). Make sure there's no static interference between your router and your computer (such as a microwave) and try turning off any devices that use your internet such as gaming consoles, other computers, turning wifi off on your cell phone, etc... Also make sure you've got some sort of encryption or password on your wireless internet.