In-dash monitor problems

I brought a 7" indash monitor and when i hooked it up the monitor comes and flips up but after about 30 seconds the monitor will flip down and turn off

It has a Red,yellow green and black wire

the red i hooked to my radio red power wire

the yellow i hooked to my radio yellow radio wire

and hooked the black and green wire together and grounded them

Does any on have an idea what the problem is

i think the brand is Innovatek  tm-705ql