|You have to remove the cover on the base of the laptop and check that the adapter unit is securely installed, and connected.|
Occasionally these items can be slightly dislodged - being a laptop. Doesn't often happen but has been known to.
This is the service manual - from the link I posted earlier:
Section 2 - specifically 2-9 onwards discusses bottom access; and the HD and wifi adapter are under the same cover.
You will note from this manual that the wifi antenna itself is actually in the lid - at top of the screen housing. Obviously it has connections that end up at the wifi module - via a pcb path no doubt...?
Again - does the adapter (still) show in device manager?
And to confirm - if you go to any other wifi access point it still doesn't detect those either?
Did you per chance do "anything" to the system that produced the problem as described as a result. Or did this problem "simply arrive"...?
Can you identify too the actual make and model of the installed wifi adapter? Device Manager will furnish that info - as will Belarc Advisor and/or msninfo32.