Yesterday, I was having problems starting my Ruby on Rails server on port 3000. This morning, I discovered the netstat utility that comes with windows.
netstat -a -bgives you a list of all running programs along with what port they're using and their process id.
This helped me to find out what was hogging port 3000. In my case the offending process was wcescomm.exe, which is to do with the Windows ActiveSync program, and just removing my PDA from it's dock released the port.
If this doesn't solve it for you, you can use taskkill to forcibly terminate a process. For example, to kill off process id 2420:
taskkill /f /pid 2420
