Dell Dimension E520 Cannot see router & vice versa

I cannot get Sharing & Network Discovery to turn on and stay on.  It will say 'click here to enable/or turn it on', but as soon a I get through those steps the  tab says 'Custom.'  I'm trying to wirelessly access the router & the internet.  OS is Vista and for some reason cannot see the router Linksys N.  I had this same computer using this same network adapter -Linksys N- work just find a few months ago.  The computer attached to router is also Dimension E520 running Vista.  For a few months I was wired (cable) separately as a business class comcast customer.  The day the comcast tech disabled the wired connection was the last time I had internet connection - 3 weeks ago.  I'm not sure if disconnecting the comcast gateway box makes any difference at all. The router attached computer is using McAfee, my wireless computer runs Kaspersky.  I've disabled firewalls, virus protection,etc. to no avail. I've check all hardware for loose connections. I've cycled the modem & router til I'm blue in the face.