First establish that you have internet access with a wired connection to the same router.
If you don't get internet access that way either, the problem is most likely with the router itself or with your ISP.
If you do get access with an Ethernet cable, then unplug the cable and check to see that your wireless adapter shows up in the control panel. If it is there and says that the drivers are up to date, then you have two possible fixes.
First open the network control panel, manage wireless networks, and delete all the wireless networks in the list, restart your computer, allow it to find all the wireless signals again, and select the one you want and enter security passkey.
If that fails to fix the issues, then change the MAC address of your wireless adapter using the free and simple app from HERE. It automatically saves your old address, and has worked for me a number of times in tough spots like this.