New monitor for my build, various problems.

Have you tried using any buttons built into the monitor, assuming that there are any? Most monitors have auto-adjust buttons build into the side or bottom.

Have you called the monitor tech support? If you just bought the monitor, it's almost certainly under warranty and you can simply exchange it.
 
Read the *** manual! "The XL2420T comes with a stylish S Switch. This distinct remote controller comes with three preset buttons so you're able to customize and save your display settings for gaming, work or entertainment purposes. Use the scroll button on the S Switch to quickly navigate and change the OSD settings. It eliminates the tedious process of adjusting your monitor settings. Now switching seamlessly between the presets is as easy as 1-2-3."
 
Hi there,

I just picked up an RL2755HM and this was the first post that popped up when I searched for the 'grayed-out' auto-config issue. Turns out, if you are using HDMI (or any digital input,) the auto-config option is disabled. The auto-config option, per the manual, was designed for analog, not digital, inputs.