Troubleshooting my WiFi - can't get an IP-address

I'm using a Samsung Galaxy Gio (Android 2.3). And I can't get a WiFi connection. My brother has the exact some phone and can get a connection. When I enable WiFi, it tries to connect to the router. It then says it's trying to get an IP-address. But fails to do so and closes the connection. When going to *#*#4636#*#* and into the WiFi Status menu it tells me the following: WiFi state: On Network State: connection lost Supplicant State: DISCONNECTED RSSI: -200 BSSID: SSID: Hidden SSID: False IP-adress: 0.0.0.0 Mac-Address: /censored/ Network ID: -1 Link Speed: 1 Mbps What should I try to fix my WiFi connection?