Logical HDMI display reconnection
You most likely need an active HDMI to VGA adapter.  There is a bunch of signaling conversion that goes on with an adapter, especially when it goes from digital (HDMI) to analog (VGA).  An active adapter will reformat the signals so it's a true VGA signal rather than just supply the correct pin outs.

Take a look at this answer, Passive vs. Active adapters - I talk about the difference and why it's important.