is it currently setup to work with your CRT and does it work ok with that?

if so, double check your graphics card settings, if your graphics card is set for a CRT monitor it WONT work with a TFT unless you tell it to before you plug in a TFT monitor, its a catch 22 situation, graphics cards dont always auto detect what you plug in to them.

Ive had this loads of times. By default, CRT is always the default monitor type.

with your CRT connected, set the graphics card to AUTODETECT the monitor, save, exit, swap monitors, reboot

if that dont work, manually set it to TFT, save etc...