Why should your team have to suffer because you are AFK and your computer has a tendency to crash? You were absent from your team for a certain period of time.
Luckily youre unranked but it certainly isnt fair to them.
The ban is a 20 minute ban to get you to realize you should probably do something about your wifi . 20 minutes is after a series of AFK events. I normally never AFK and in the past 2 days I afked twice just from the tilt of my games. I didnt receive a ban but I had a warning. When I first started league of legends I found it to be such a boring game I afked 10+ times in a week and went from a warning, to a 5 min ban for 5 games, then a 10 minute. 20 minutes means this is the norm for you and not something lightly. If you want to waste your team mates time by being afk and costing them the games, enjoy the ban.
Im sorry if you have financial issues and cant afford a new computer (not sure if this is the case), but it isnt fair for the rest of us to be held back either.