How are you connected to your Router now? Or is it for a different computer? Is it a Desktop or Notebook?
If connected by Ethernet cable try right-clicking the Start button, click Device Manager then click the little arrow on Network adapter entry to expand it. If you see an entry for WLAN check that it is not disabled then right-click it and update the drivers. It may be possible it's a Notebook that usually has a hardware method of turning on or off of the adapter, a switch or an Fn + Fx key combination.