I have two systems (one at home, one at the lab that such happened. I scrounged up some network cards to fix this issue since downtime was more expensive than adding a NIC. What might help is latest driver for the system. I know you write up to date drivers, but some rely on Microsoft with it's Windows Update or Driver update and that's not good enough.
Best of luck,
if i let computer alone say 2 hrs or so i have no conection. if i click on my network conections and repair it im fine??
all drivers up to date motherboard etc. spyware free trojan free virus free
xp pro fully updated
512 ram 40 gig hard drive useing 8 gigs of it:(