If you can ping your router then your network is not really down. I assume the problem is that you cannot access the Internet, correct?
This sometimes happens to me and I seem to be able to recover by
- Unplugging the power supply for both my router and my ISP's cable modem.
- Restoring power to the ISP's cable modem and allowing it to power up and initialize.
- Restoring power to my router.
Have you tried that? (Assuming it applies in your situation.)
It would help us to answer if you updated/edited your question and provided more details as @Huygens has already requested.
Another thing you might try is running the following command in a terminal window:
dig www.askubuntu.com @18.104.22.168
The result you should get should look like this
irrational@BlueUbuntu64:~$ dig www.askubuntu.com @22.214.171.124
; <<>> DiG 9.8.1-P1 <<>> www.askubuntu.com @126.96.36.199
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 861
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.askubuntu.com. IN A
;; ANSWER SECTION:
www.askubuntu.com. 1942 IN A 188.8.131.52
;; Query time: 46 msec
;; SERVER: 184.108.40.206#53(220.127.116.11)
;; WHEN: Tue May 8 18:21:34 2012
;; MSG SIZE rcvd: 51