How to make HD bootable?

So I am installing Puppy on an old Compaq M300 laptop, which has no CD or floppy.

So I took out the hard drive, put it into a USB enclosure and installed Puppy from my desktop.

When I put the HD back into the laptop, it wont boot. Puppy offers to create a boot floppy, but I cant use that option. Is there a way to set the hard drive to boot itself?

(I am newbie to Linux so bear with me)

Would it make a difference if I unplugged my desktop HD, which would make the USB/laptop HD to be an "a" partition?

You must have a properly installed bootloader. We use Slackware here, which uses LiLO. Find out what Puppy uses (LiLO or GrUB), then <Linux> Google it.

I would suggest using the Puppy Linux Discussion Forum
as I am most certain this question is answered and if not I'm sure your question will be answered there.
I hope this helps.