|There are some occasions when the wifi adapter needs a little attention.|
Typically - and in no particular order...
Reboot the router (do NOT reset it).
Double check what channel your router is radiating on; and if your wifi is set to auto (it hunts for and uses whichever channel it finds the router is using - if it can) - or manually to the same channel as the router.
Check in Device Manager to see if there are yellow exclamation marks against the wifi adapter (in the Network adapter branch)
Upgrade the driver for the wifi adapter.
Maybe even "uninstall it and then re-install; and allow windows to check for an updated driver.
What make/model number wifi adapter is in your laptop?
Have you installed anything about the time the system seemed to degrade re' wifi?
Have you tried a restore point?
The last two ideas are really not very likely of any impact if you can't actually detect the signal in strength..