You will not lose everything if you reset your password. You would, however, lose everything if you reset your router to its factory-default settings.
Network devices (TV) only require the frequency of your network (2.4 or 5 GHz), the name of your wireless network (SSID) and the encryption key of your wireless network...if that's what you mean by "password." If you wire your TV, you won't need the frequency, SSID and key.
You're probably entering the wrong key into the TV.
How does your TV respond after entering your network credentials?