A little more information on how you installed might help. As far as documentation,
http://www.slackware.com/
might help.
My guess is you have linux dual-booting with windows. If so, you'll have to set windows and linux up in yourboot loader. Also, you might not have set up a bootloader, and that might be your problem as well. Check grub/lilo sites to work on this. One note, if you're using winnt, win2000, win2003, you might have to set the linux bootloader on the partition that you are using for linux, then use the windows bootloader to actually run those.
Unfortunately, I gave up on windows back in late 1998, so I can't step you through that procedure.