the GUI is also broken... ok
Can you try and run startx command as root? to see if the GUI is working as root? if yes then go to your home account delete all .serverauthXXX and .Xauthority files as root.
Also did you install Slackware as a full install on the installation steps?
Can you please also give a try to install the exton kernel
to see if the newest kernel will find your card
If I was you I will give one more try to reinstall slackware from the start and follow the first step the one I told you the chmod +x /etc/rc.d/rc.networkmanager for your wifi card (do a reboot after this command)
Then follow the instructions
1) to add user
2) to select mirror
3) update Slackware
I dont know what you did exactly I am just guessing. Slackware is my best operating system and you should give one more try and you will find your way. I was in your position too when I was trying to do my first Slackware installation. It was a nightmare :) for me too but I learned a lot of things using this particular operating system. Good luck my friend