Dropping out of networks can be caused by various things: faulty device, transmission rate, distance between client and Internet source, configuration, etc. In your case, you will have to check all those things.
Open the management software and reset everything, including settings, networks, adapter, etc., then reconnect.
Go to Device Manager (Start > Run > devmgmt.msc) and check the driver's installation. Re-install it if it appears in yellow.
Check the router and increase its transmitting power to 100 %.