Network fine - Internet not

I have a network using a cable modem through a router, and downstairs a hub.
All computers (XP and 98se) have been working fine, but when I took out a 98
computer that hadn't been used for a while, it would not connect to the
internet. It sees all the others in Network Neighbourhood, and shares files
ok, but AVG can't update, and dns error page with browser. Won't connect
with ip address numbers in the address bar either. Won't even connect to the
router. Then, another computer I tried did the exact same thing.
Funny, they both worked fine last time used, a month or two ago. File &
Printer sharing enabled, same workgroup as others, share level access,
Client for Microsoft Networks.
I have rechecked all settings (to use dhcp, obtain ip auto, etc.), I
uninstalled/reinstalled TCP/IP, even uninstalled/reinstalled dialup
networking (deleting winsock2 reg key). Shut Zone Alarm right down. Tried a
different cable & jack in the hub that worked fine just before w/another
machine. Reset the Belkin router. ipconfig released & renewed. Various other
"fixes" I can't think of right now.
NIC's are both IBM 10/100's that always needed Auto changed to 10 baseT full
duplex in order to work on this network, with NetBeui, for some reason, but
always worked fine with that. Funny thing is no settings were changed since
both these boxes last worked fine when I first had the problem!
Any help is greatly appreciated! Thanks.