Try this instead:
Shutdown / power off in Slack
Slackware does not power off by default as you give the command ¨shutdown -h now¨.
To address that problem:
# vi /etc/rc.d/rc.modules
Look for the APM section and
uncomment the line ¨# /sbin/modprobe apm¨ ( delete the # )
Save the file ( give the command /sbin/modprobe apm if you don´t want to reboot ) and next time you do ¨shutdown -h now¨ as root your computer will power off as usual.
Hope this helps,