PC to PC: on-off-on-off etc.

2 PC's, P4's, both MSXPpro, SP2.
Linked via LAN plug and cable to hub.
The Host PC was for repair and they had tochange the MB, but managed to load
also some settings from the setup with the unserviceable MB. One can look
from the host-PC into shared drives in the client PC.
Put whilst both PC are on, suddenly from the LAN icon is a message "a LAN
coble is unplugged" and after 2-5 seconds, the "PC1 is connected". And that
repeats quite frequently.
Must I de-install all sharing and remove LAN cables and start afresh or is
there a shorter route?
Is ist a must to map network drives? Because thos are not mapped on neither
PC.
Greatful for any help.
Regards
nopfusch