I installed Ubuntu 12.04 LTS for my mom, this runs OK.

However recently, I switched back and forth between encryptions on our WiFi Router from WPA-PSK to WEP and back again to WPA-PSK, same password.

Now this old laptop won't even ping the gateway on the router, although the nm-applet shows connected.

I tried re-adding the network and putting in the BSSID. I did this over again sometimes just to verify.

I tried with my 3G Tethering on my phone, it works fine, can go online too.

My other Linux laptop can go on the same wifi as well as my phone.

And this laptop used to been online on the same network, same password, same encryption (WPA-PSK)

What can be wrong ? Does it need a serious kick in the butt or removing some cached authorisation somewhere?