Thunderbolt is not working with vga adapter

Hello, I search a lot of things about Thunderbolt and external displays but it was not enought.
There are three ports, two Thunder and one HDMI, i have a HDMI monitor that works with HDMI port,
i`m trying to use the Thunderbolt port with a VGA monitor by using Thunderbolt-VGA adapter but this is not working,
my monitor is not showing any images and the mac mini is not recognized the display to. Maybe the vga port is not workin
i dont know. There is a dvi-d port to on this monitor and i test with the HDMI port on mac mini and its works.
There is something about the yosemite system that cant be work with VGA and only hdmi-dvi-d and others?

thank you

I would believe the vga port on the monitor has stopped working. Have you tried another vga cable?

YEs i tryied with two vga cables, i do not have other monitor to test.. i tryied to download mini display port update firmware and nothing happens

I guess we need to ask... but why would you even want to use the VGA port on your monitor? VGA is analog while HDMI and DVI are digital and will deliver much better quality. Also, most modern monitors no longer include a VGA input.

yes yes, u right, but i have a logistic problem, i can use hdmi-dvi-d on this old monitor, my newest monitor has hdmi and dvi-d, and i have to buy a new cable thunderbolt-hdmi or thunderbolt-dvi-d. So, i prefere to use hdmi-hdmi on it and buy a thunder-vga or dvi-d for the oldest monitor. considerying that the vga female may not work, i`ll buy a vga-dvi-d adapter to test on the dvi-d port that is working regulary.
thank you for this conversation, sometimes when u ask a question the solution can appears in your mind.