Link problem on Dell laptop, Broadcom 4401 network interface

A lady at work has a link problem with her inspiron 5100 laptop, which uses
a Broadcom 4401 interface. On occasion she just loses link, and I have not
been able to figure it out. So far I have:

Replaced the cable from the wall to the laptop.

Tested the full cable run from the hub to the connector that goes in the
laptop, with a Fluke DSP-4000 cable tester. If this tester passes a cable
run, it should be good.

Replaced the motherboard in the laptop (which has the NIC built in). A
local repair guy working for Dell did this. He upgraded the firmware as
well.

Odd eh? The hub is a Netgear 10/100 24 port hub and nobody else has any
link problems. The problem is that the link light will go out on the hub,
and on the laptop, XP reports a cable is disconnected. I might go back
today and replace the jack in the wall just to be sure its not a mechanical
problem that wasn't happening when I tested the cable. Other than that I am
not sure what else to check. The problem occurs while working so its not a
power management issue with the nic. Does anybody have any suggestions?

THANKS!
--Dan