Well you said yourself you didn't check the checksum. Something could have corrupted the download. Why is your laptop semi-dead? Maybe it is a hardware issue?
Run the the command: lshw -c network
Copy and paste the results here.
That command will give your WIFI card information. Again more information is needed. Make and model computer is needed too.
See post: Need help with configuring wireless network on Ubuntu Mate - #2 by jymm