Is your wifi network LED on? If so, and wifi doesn't connect to your router, did you power cycle your router & modem?
Have you processed the steps on page 123-125 in your manual?
If so, then you probably have a hardware failure. Your LT may have a replaceable WiFi card. It would be under one of the removable panels on the bottom. If so, you may be able to find a replacement.
A 14 yo LT may not be economical to repair.