If you keep having problems with Wi-Fi, it is almost always down to your router settings.
This should be set as follows:
The router should support Wi-Fi b/g. Set your modem in to Wi-Fi b/g, or Wi-Fi b/g/n.
Select a fixed channel; do not let the modem automatically choose a channel. If you have selected a fixed channel but there are many networks in your vicinity there is a possibility that your chosen channel has a weak signal and is being suppressed by the environment.
- Try other fixed channels to see where the strongest connection is (some routers also give a problem on channel 13 for example).
A DHCP server must be active on the router (or elsewhere in the network). Instead of the WPA/WPA2 combination, use only WPA2.
Select WPA2 with PSK as security and AES (no AES + TKIP) encryption.