Well if /boot is empty, then no kernel is installed, and that's a pretty big problem. It's part of the base system (section aaa). You need a kernel installed, and then run liloconfig and follow the guide to install LILO to MBR.

If you're booting from a USB drive and aren't able to pass the "root=/dev/sda5" option at boot time, then yeah, installpkg ain't gonna work right. How 'bout try this...after booting, run "setup", and go to "Add Swap" and once you've set up your swap partition it should take you through the rest of the installation. Tell it which partition is to be mounted as / and blah blah, and this time choose "Full" installation. Then wait for everything to reinstall and afterwards some config scripts will get run, liloconfig being one of them.

Maybe that's a bit extreme for your situation, I don't know. But I really have no idea what you've installed and what you haven't or what's going on.

...and then go to slackbook.org and read, read, read. You'll learn a lot about slackware.

Wait....I'm sorry, of course /boot is empty, you've booted from the USB drive, duh. Heh sorry, It's like 3 in the morning here and I still can't sleep.

How about this: boot up from the USB. Then mount /dev/sda5 and the rest of your partitions somewhere, such as /mnt. Then do a "chroot /mnt" and hopefully /boot won't be empty there! If things are looking good, now try liloconfig. Still no? Then mount the USB filesystem and installpkg the lilo pkg, and then try liloconfig.