When this happens, are your other devices still connected to the wireless, but can't access the internet?
From your computer try pinging the router and see if it responds. If it does, try access the routers web interface. If you don't know the routers IP address, just type in 'ipconfig' in a comand prompt and check what your default gateway is - that is your routers IP address.
If that works, try pinging
www.google.com, and then ping 8.8.8.8.
Good first steps to check for any network issues - helps if issue is just access to the internet, or affecting local network as well, and also can rule in/out DNS issues.