Is my HDD dying?

I have an HP ZX5180 US laptop running xp pro sp3. The other day it shut down and tried to restart and all I got was:

PXE-E61; media test failure, check cable
PXE-M0F: exiting PXE now
It was running in a continous loop

I googled that and understand that the computer is looking for a network connection because no physical drive exists. So I shut it down and left it for a few hours. I tried to start it and low and behold it booted fine, ran for a couple hours and then returned to the previous mentioned state. I removed the harddrive and it wasn't unusually warm or anything, I put it back in cleaned all the cooling fans, sinks and passageways. Restarted it and it ran fine for about 10 hours and boom shut down restarted and gave me the following error:

A disk read error occurred, press ctrl-alt-del to restart your machine

It continued to give me the error over and over. I let it rest (cool down) for awhile and put my ultimate boot cd in the dvd drive and restarted the machine, after a couple of hours it shut down rebooted the boot cd and ran fine on it. There was no physical drive after windows started from the cd.

Long story, my question: Bad HDD or bad connector on the motherboard? I know it must be getting hot and shutting down, after awhile it cools and boot fine. Scan disk found no physical errors, BIOS reports the HDD as fine, I would hate to spend the money on a replacement drive if it is the motherboard. Any ideas?

Thanks
Dave