If you plugged it into the internet with a public IP, someone would likely gain full remote control of the machine in a matter of seconds to hours.
You might think you’re safe if you only connect to your home internet, since that’s not wide open for anyone to scan. But then your kid/nephew/friend uses your wifi and they have a spyware-filled Doodle Jump game clone on their phone that asks for permission to connect to the local network, and your kid/nephew/friend wants to play the game so of course they click yes, and now that’s scanning your home network, and now your Windows 7 computer is part of a botnet.
The same thing would happen on the coffee shop’s WiFi, the hotel’s wifi, and so on. Unless you never connect to a network of any kind ever, it’s a bad idea.