If your machine's BIOS support booting up from External device then I would suggest you to disable Internal disk in BIOS and re-install PCLinuxOS or any other distro of your choice in External disk.
I have tried disabling the internal disk from the BIOS and installing Slackware which is the linux distro that I want to run. I selected the installed LILO to the mbr but when I select my external USB drive (which is a Seagate FreeAgent USB drive) as the first device to boot from in the BIOS I get the following error:
GRUB Loading Stage 1.5

GRUB Loading, Please wait...

I really don’t understand why because I would have expected GRUB to have been overwritten by LILO.
If I select the internal drive as the first boot device, I get to a LILO menu which ask me if I want to enter Windows or Linux (Slackware), upon selecting “Linux” Slackware start loading but it then gets stuck guiving me the following message:

VFS: Cannot open root device '813' or unknown - block (8,19)
Please appened a correct “Root =” Option; Here are the available partitions:
0300 4194302 HDA Driver Columns IDE - CD ROM
0800 117220824 SDA Driver Columns SD
0801 110928793 SDA 1
0802 06289447 SDA 2
Kernel Panic - not syncing: VFS: Unable to mount root FS on an unknown - Block (8,19)
I suppose is not recognizing my USB hard drive or something like that