Cable unplugged msg in winXP

My home network consists of my PC with a cable modem, my flat mates PC, and my girlfriend's PC, all three are running WinXP Pro, and they're conntected together using Cat5 cable that we laid and wired ourselves (we just clamped network plugs to the end with the correct tool using a map we found online). They're connected together using an intel inBusiness 8-port switch. In the past the network has worked perfectly using winXPs internet connection sharing to share the cable modem access. My girlfriend's computer is a recent addition to the network, and worked seamlessly for a couple of weeks, until a couple of days ago her light on the switch went out and winxp spat up a cable unplugged message on her machine. I've tried unplugging and re-plugging in both ends of the cable, and tried using a different port on the switch. I've checked both ends of the cable and the wiring *looks* fine. I've checked the cable along almost all of its length (in all the places that are easy to get to where it might have been severed or damaged) and it appears to be fine.
In her computer I have a K7S5A with onboard NIC, and a Voodoo3 (there's 256 meg DDR, and a 1gig duron, but I didn't think that was likely to have any baring on this!). My course of action was going to be in the following order:

check the settings for her onboard NIC
reinstall the drivers for it
check the entire length of the cable
install a proper NIC and disable the onboard one
rewire both ends of the cable with new connectors
replace the entire cable
smash the whole lot to pieces with a big hammer and take it to the tip

Well... I may skip the last phase, but I may have actually gone completley insane by that point. Does anybody have any other suggestions? Before anyone suggests it, I don't think I can get hold of a cable tester and the cable goes through two walls and covers two floors of the house, so getting both ends together is going to be less than easy!
Any suggestions greatly appreciated.

Cheers,

Thorin