Changing route (and IP address) crashes Win 98 PC

I have not been able to figure this out!

I want to change the router on my LAN. I also want to change the IP address
to enable a VPN connection to complete behind another private network
(currently using the same subnet).

When I switch the router out and the IP address changes on each computer,
all is fine on each workstation, both Win 98 and Win Xp. This is with the
exception of one Win 98 workstation. This workstation blue screens after a
few minutes.

Please advise.