I have a Studio XPS 8100 running Window 7 64 bit.   It has a WLAN PCIe Card DW1525 (802.11N).      I have a wireless network set up in my home with a Airport Extreme Router.    The Wlan card gives me little or no connectiviity and will not stay connected.   The majority or the time it tells me there is nothing available

I have a Precision 4500 that I can put at the some location and it connects and stays connected with no problems and full bars.

I believe that this means that there is a problem with the WLAN.

I also have a Verizon wireless mobile internet which I use with my IPAD and  I can set directly by the computer and it will only pick up 1 or 2 bars.

Is anyone able to tell me if there is a way to fix this or even what the problem might be? 

I have tried disabling the Norton firewall and it does not help.   The Windows firewall is controlled by Norton.