is it a wifi connection from the laptop to the router? if so, have you accidentally turned that off on the laptop? that used to happen to me occasionally
Resetting the TCP/IP stack (which sounds complex but is actually very easy to do) fixes the majority of such problems. Simply click the relevant 'Fix it' button here:
http://support.microsoft.com/kb/299357
PS: My post assumes that your laptop can connect to the router but not to the internet. If it doesn't even connect to the router you might need to reinstall the Wireless LAN driver.