If your wireless router is still turned on and connected then it should be visible as a wireless network.
It sound like your wireless adapter is the device thats missing from the device manager. Go to your laptop manufacturers website and download the wireless lan driver
for your machine.
Make sure the wireless adapter is switched on, this is often toggled by either a switch or button on the laptop, or with an FN shortcut with an icon similar to -> ((i))
Install the driver.
If your wireless adapter is installed and working you should just search to join an existing wireless network. If you are able to search for networks but cannot find your, try connecting to the router via a network cable and changing the wireless setting on the router.
EDIT: Just realised I told you to go online for a driver when you can't connect to the net. Just check device manager for you wireless adapter, if it's not there it's probably switched off. If it's got a yellow exclamation mark then you will need to get the driver from somewhere and use CD/USB to move it over.