default gateway not available.

I had bought an Inspiron 15R SE 7520 last year & upgraded to win 8.1 two months back. My wired Intenet was working fine till 25th August but suddenly it started showing Unidentified network and on troubleshooting the network it shows Default Gateway not available. Tried nearly all solns. on net:

1. updated my realtek driver

2. checked device manger

3. disabled the firewall

4. Manually enterd he ip for the connection

but to no avail. can anyone pls help solve this issue as it is so annoying. the same internet works on my old win XP laptop.