You might have the port blocked by something which could prevent your server from listening on port 50000.
The netstat tool might be able to tell you if this is the case. Then you can use the PID of whatever process is blocking the port to forcibly end the process.
I'm not sure if Windows firewall is capable of blocking anything on localhost, but that might be worth a peek as well.
Forget about video drivers or HTML5 trouble. From what the browser is saying it's clearly a networkish problem.