Connection/Latency problems - weird symptoms

So i was playing with a few friends using a ts server, a friend of us has set up. The server is located not far from my place. Everything worked out great, then i had to change to my router and right after a few seconds the package loss climbs to 80 % and i lost connections to the server. This doesnt happen always but in 90 %.

Ok, so my router seems not to be properly set up, BUT my wife can connect just perfectly by using her Mac going through the same router.
Besides i can join any other Teamspeak-Servers without any problems.

Ok, so the server is not working properly. Well everybody else from around, even people using the same ISP, can join just perfectly.

I tried opening ports, asigning a fixed ip, checking my windows firewall, optimize by using ccleaner and running a virus scan. I just cannot seem to find the problem, why this specific server does not want to communicate with my specific machine. Actually most probable reason for the problem should be my machine, as everybody else, even my wife using the same router can join and talk. But then, what is there to change on my machine/in the teamspeak settings, since everything was working before router change.

Help would be appreciated

Connection/Latency problems - weird symptoms