I am assuming the wifi does work again for e.g. your laptop, after your replacement, just not for your tablet.
If you replaced the wifi-router-and-modem, and set it to exactly the same network name and password,
on your tablet you STILL have to remove ('Forget') the old connection and add it newly.
Your new router-and-modem may have a tighter security setting than the one before,
it may for example want the MAC-adress of the tablet to be put in some list.
Did you set up the new modem-router yourself?
