Hi,
Unfortunately, not real familiar with the VG248QE myself, but was checking the user manual and noticed there is an 'input source' button on page 10 as in the screenshot below, so just wanted to make sure you tried cycling through all the monitor inputs which it sounds like you may have.
You might also try connecting by HDMI just to make sure this works at least or making sure the monitor works with a different system to get a better idea where the problem is coming from?
Well, hopefully others have better ideas if this doesn't help.