I recently installed Ubuntu 12.04 in my Dell Inspiron-5520 laptop. Though everything else seems to work properly the wireless network doesn't seem to work which worked perfectly when I had Windows 7 installed. I also tried connecting to internet using a wired network and that too doesn't work. Please help me as I am new at this. I might be wrong but I think there might be a problem with my network drivers. In any case my laptop uses BCM43142 chipset.
I suggest you upgrade to 13.10 it supports your wireless card by default, then run the following commands:
wireless should come on, if it does not please post the wireless info again from the script so we can see the current state of your wireless.