Imac a1224 2266 screen backlight issue

Hello my screen on my imac 2009 20" a1224 went blank and would not come back on. When you press sleep it flashes and yu can see everything but goes straight back off again.

I turned the brightness right down and sometimes the screen will stay on and can use as normal.

I have changed the inverter board but it's still the same.

I heard of resetting the smc but I don't have an original apple keyboard only wireless one and don't think it's doing it.

Any help would be very gratefully received.

ThanxShane