Have you got the literature which came with the router ? Or download the full manual from the maker.
Has the router's WAN side been set up with your internet supplier's
recommended settings ?
If so, now worry about the LAN side. Connect an ethernet cable between the computer and router.
You need the IP of the router (often 192.168.0.1 or check by using IPCONFIG /ALL in a DOS box from Command Prompt). Put the IP into the address bar of your browser and you should then see a login box -- the user name is always admin. The password may be left blank or be something like password or admin -- see router literature.
Once in go to Wireless settings and check that SSID is being broadcast not hidden, that wireless is enabled, that wireless mode is g or n or mixed mode (depending on the type of wireless adapter in your computer).
In Wireless Security select no security for the time being.
If there is an option for something named Access List or similar (admit or refuse by MAC ID) disable it.
Save settings and log out.
Disconnect ethernet and see if you can get back in to the router setup via wireless.
If success, restore wireless security settings in router and apply same to wireless adapter.