How to recognize a computer

I'm trying to use TeamViewer to control another computer. But it won't recognize that another computer exists. The other computer is connected to my router, and it has internet. So what am I doing wrong?
Ok, I have the software installed on both computers. My computer still doesn't recognize the other computer. It says "a connection could not be established. reason unknown"


Essential Member're killing me...seriously.....Both PC have to have the software installed, both have to have the software open and running. The host PC (yours) needs the password from the 2nd PC.