I have an Acer Iconia tab w500 running Ubuntu 12.04 - The only output I have is an HDMI output so I bought an HDMI to VGA cable to connect it to my external monitor. It's not being detected by Ubuntu. Please let me know what other information you would like me to provide. Thank You!
It will not work since HDMI is digital and doesn't support analog signals.
You could use an adapter.
There are two kinds of DVI signals
So if you hook in the VGA → DVI cable, the signal will be analog on the DVI-end of the cable.
Since HDMI is digital, it doesn't support analog signals.
Extracted from here.