ZDoom

So I booted up a "Registered" wad of Doom (No idea what the difference between the Shareware version and the Registered is) and it has massive input lag, I'm talking 3 seconds after I push the menu button before it goes to the menu. How would I fix this?

Which version of ZDoom? What are your specs? Which renderer are you using?

I figured it out it was GZDoom v3.1.0 (Windows 64bit) and I just went in without checking the usage, and it was in an OpenGL thing, I switched to the source option and it works fine now. No idea why it caused massive input lag though, also I figured out the difference between Shareware and Registered.