Welcome to LQ!
Your post is short on detail, but what you describe sounds like the sort of problem that occurs with drivers for some Intel graphics chipsets.
This thread provides details:
To help further requires more information:
What version of Slackware are you running?
What is your graphics? (Look at the output of 'lspci')
What Intel driver are you using? (Look at the output of 'ls /var/log/packages | grep intel')
Be warned, the best fix will probably be to upgrade to the latest Intel 2.9.0 driver and the latest stable kernel 126.96.36.199. This will be a challenging task for a noob, but you installed Slackware knowing this could happen and can embrace this, right? :-D
As an alternative, you could try specifying the vesa driver for your graphics in xorg.conf. This will provide stability, but will be a little sluggish and not allow for some eye candy features.