My Raspberry Pi is active on my network and I confirmed that it's online with an IP scanner. But if I run PuTTY (I usually connect through SSH instead of HDMI) and try to connect, it says that the hostname doesn't exist. Is this a problem with my Raspberry Pi or something else?
Thanks, Jaromanda X. My problem is now solved by using an IP address instead of the hostname. I'm using Windows 10 with PuTTY to connect to the Raspberry Pi, in answer to your OS question.