@Rits To reset the administrator password of C64 follow the instructions bellow: After resetting the device you'll have to re-configure it from scratch.

@nrajeshgoud There's a newer FW for your device. You can upgrade the FW (Case 1) and check if that can help with your issue. If the issue persists after the FW upgrade try switching the IGMP version...

@WEEP Your only option is to use the QoS feature (Case 2) for prioritizing the internet traffic of your devices.

@Eariss Login router's web management interface http://tplinkwifi.net/ and try these settings:

@Artchern When router is powered ON use a paperclip or toothpick and press until you feel/hear a click:

@Clem_Viking The web interface is different, because I used another TP-Link device just as an example - you didn't mention what model is your DSL router. In your Internet connection=>Advanced...