DNS server not responding...

So after the change of the WEP encryption key, there is another issue that emerged out of nowhere again. This time it's the DNS server error, and other windows in our house can connect except for me. I can enter the security key this time however the wireless icon indicates a exclamation mark icon overlapping it. I tried using cmd and typed ipconfig /flushdns, ipconfig /release and ipconfig /renew with a reboot afterwards, changed the Internet Protocol Version 4 and 6 on their DNS server address settings, reseting the router and configuring the network adapter but it doesn't work. Although, the window 7 can sense the internet and connect it but the result came up "DNS server error" and "DNS cannot communicate with the resource error".

I currently don't hold the real password for the router, however I managed to retrieved the old WEP password for the router. My cousin has the password, whenever he types the password now which I don't know at this stage doesn't work (Security Key Mismatch) and when I secretly tried the old password, it worked but with an exclamation mark on the wireless icon.

Any of you guise know what the hell is going on with the router or my window 7?
Sorry for the rant, because I'm starting to fed up with these kind of issues.

^
Greetings

Wait but I thought you can only enter the right characters in order to connect to the wlan. Any wrong passphrase would still result into the security key mismatch error dialogue box.

The router changed from WEP to WPA2-personal by the way, I apologise for the vague description I gave in earlier.