You aren't being descriptive....

1. You burnt the ISOs. Did you burn the iso "onto" the cd itself, or did you just put the .iso file onto the disk? (I'm assuming you burnt the iso right onto the disk, but just checking)
2. "Installation screen didn't come up"? Like, did you get the boot prompt? Hit return, and then you'll be dropped at the shell. It's up to you to manually partition your hard drive and mount the newly formatted partitions. Then you start the install process with "setup" I think.

If you can't even get it to acknowledge that Slackware is loading, then maybe your CD is faulty. Try burning another one. If you're sure the CD isn't the problem, check the BIOS settings again. (Maybe a "reset to defaults"?).

Here's an installation book for Slack:
http://www.slackbook.org/