Here is What i think You Should Do while Having issue With Brother Printer Wireless Connection
1- First Restart Your Router And Brother Printer ( if possible Your Computer Too).
2- Make sure You have the right password for Your printer.
3- You Can Try WPS Key to Connect your Printer with Router if your router and printer does have a WPS key.
Now Uninstall Any previous Printer Driver if you have Installed and Install Your Printer Like Brand New.
Since you are Going to Install it like New One Please Follow These steps to Install the Brother Wireless Printer Please Visit How to setup Brother Printer
See if all this Information Would Help You setup the Printer and Help You Get rid of the Issues You Are Having.