Same Problem here with a i5-2500K and current onboard-drivers.
If i deinstall em and use generic Windows-drivers, i am able to tune up to 1080p and everything works fine. But my DVB-Viewers are just stuttering. So far i have tested two 46" 1080p LED-TVs and two independent Cables. Via DVI my normal Office TFT is running just fine, so it is a Problem of the Driver. Please Intel, give us some clues. This Problem gets reported every now and then and still you have no idea were it comes from?
this is a know issue , some people i seen online had problems after driver update, but i didnt do nothing. Your in a better situation then me, I dont even get an image even during post. I got the vga to work but now im stuck using an olt crt monitor from 2000. Dvi and hdmi still dont work. I contact intel, they said update to latest driver, had no effect, they also told me to contact my computer manufacturer, which is gigabyte since i bulit the pc my self. So contact gigabyte and even though it has been less then a yr since i bought the mobo, they want me to pay for shipping to get the faulty mobo back to them. My son just had a problem with ps3 and sony sent him everything he needed to send it back to them and they paid shipping. So its not even worth it for me to send them it since i could probably go get a cheap gpu and hope that that works. For anyone who is thinking about combining intel i5 2500k with gigabyte mobos, DONT DO IT unless ur going to use dedicated graphics.