What are the causes of "No Internet Connection"?

[Josh Bommer]

About an hour ago, I went through "heck" just to get my internet connection working again. I managed to do so, but can anyone give me a list of the stuff that causes "No Internet Connection"?
Also, does the things below cause "No Internet Connection"?

1. Downloading video games, music, videos, and software online.
2. Staying connected to the internet every single day and night.
3. Disconnecting from the internet manually.
4. Leaving the PC on (not shutting it down when you're done with it).
5. Disabling and enabling your network connection back and forth over and over again (trying to fix it).
Thank you so much for your answers!