I think if you said you can contact your ISP you mean that it is working.
The error you mention is typical of not having a default route.
I guess you have the IP they gave you in already. Thats the first line below. If not you can do this:
ifconfig eth0 18.104.22.168 netmask 255.255.255.0
Substitute you Ip and Netmask and interface.
[david@xxxxxxx david]$ /sbin/route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
22.214.171.124 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
126.96.36.199 0.0.0.0 255.255.255.0 U 0 0 0 eth2
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 188.8.131.52 0.0.0.0 UG 0 0 0 eth0
See the line with UG, that is the gateway server. Without it you are lost. To add it do this:
route add default gw aaa.aaa.aaa.aaa
If it is there and wrong number in address do this first:
route del default gateway
this should set the default route for you, you need to put in the correct address for you isp's default gateway, where a is.
If everything goes well you should now be able to ping a computer on the web or type in an address in browser like http://184.108.40.206
and get Redhat home page. But you need to setup DNS to type www.redhat.com.
You can do this by editing /etc/resolv.conf
using the address of your name server.
then it should work.