So, you're trying to use a VGA splitter to get dual monitors? Does your GPU have 2 seperate VGA (or HDMI or whatever you are using) ports? If you're just using a splitter to split the signal onto 2 screens, then it is weakening the signal because the GPU doesn't know what you're trying to do so its not sending out strong enough of a signal to display on 2 seperate monitors.
For dual monitors you need to plug each screen into a seperate port on your Motherboard / GPU.
When you turned one of the screens off while both were connected, it didn't affect it because turning off a screen doesn't stop the mobo/gpu from transmitting a signal to it, it just turns off the display, so it was still splitting the signal strength to each monitor, however when you unplugged one, that screen was no longer receiving the signal so the other monitor was receiving the full signal.
All of this is mere speculation.
Instead of using a VGA splitter, plug each screen into a seperate port on your GPU, or if your GPU doesn't have 2 ports, plug 1 into the GPU and 1 into your motherboard (if the motherboard has onboard graphics) or if your mobo doesnt have ob gfx, install a 2nd GPU.
