I built my own system, and have been using it for about a year and a half with no errors like this. It has windows 7, and I just updated the drivers 3 weeks ago. I decided to play some Minecraft with my brother on LAN. After maybe an hour, the screen started to freeze for a few seconds. It did this for 10 minutes every two minutes or so, every 2 minutes. Then an error message appeared. It said something like "AMD --- not responding" or "AMD --- has stopped working properly", and the whole system froze! So I manually shut it down by holding the power button. Now when I turn it on, theres no signal to my DVI monitor. I don't know what to do, this is so sudden.
I'm using a Radeon 270x graphics card with a DVI cable.