hello there! it seems that this problem is not been resolved yet bcos i found the "connect automatically" option and every time i restart my phone the wifi address asking for the password again. Help meeeee
Another issue might have to do with DNS. You might want to change your DNS server settings from the defaults provided by your ISP to something else such as Google Public DNS or OpenDNS. I had issues with my phone getting disconnected from my network when I had a WP7 and used my ISP's DNS servers. Changing DNS servers eliminated the problem.
The router's IP address will probably be 192.168.1.1 or 192.168.0.1 (although some routers have different IP addresses). Enter the IP address for your router in the browser address bar, enter the administrator name/password for the router, and change DNS servers provided by your ISP.
One other issue I previously had was my router changing channels disconnected my Nokia Lumia 900.
The default setting was "automatic", and whenever the router changed the channel, my phone disconnected. I set the channel to "6", and no disconnections occurred anymore on that device. I've since switched phones to the Nokia Lumia 920, but none of my devices get disconnected since my router channel has stayed at "6".