Here is my gues...

Go to command prompt and type in IPCONFIG.

Should get something similar:

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1

If first three octets of Default Gateway are the same as the first three in IP Address then this is correct and not the problem. If they are different then your ISP has to change this. I run in to this quite often were I work and usually has to do with them trying to block unauthorized access or computers suspected of containing the most recent viruses.

If this isn't the case then replace the NIC and if it still doesn't work then you know it isn't the NIC. I would try replacing the cable as well because this can cause this type of issue. Try doing a tracert to any ip address out there and see where it fails. If all else fails then I am not sure other than the routing issue.