I was reading an article on yesterday on this subject . Depending on the strength of your Wireless signal and distance between computers and any obstruction to the raido signal between wireless points ( walls , piping , water boilers , electric cables , etc ) the receiving transmitter might lose 20% connectivity with no obstruction , with obstruction it can become unusable .

I had a netgear G series on a 20mb connection - connected full capacity wirelessly sat next to the modem and router . I tested the signal drop range by moving from room to room - in some cases I barely got to the front room door and the signal became unusable . G series is for speeds of upto 20mb . I've upgraded to an N series with 50mb .

Are you setting the connection correctly to the internet gateway device ? ( Router )

Try disabling the LAN connection in Network Options in Control Panel and resetting a new connection to the Router - All Router info can be found using the IP address 198.162.1.1 ( might change with various routers ) . Make sure all router and modem information are correct and match and try connecting .