I looked through the wiki, but I'm not sure if my problem falls under any of the listed categories.
Usually in the middle of a game or even when I am attempting to log onto the HoN server, my screen will completely freeze, showing nothing but grey/black vertical lines. The only thing I can do about this is to manually restart my computer. Sometimes my computer will simply shut down itself. I do not receive any error messages. Does this problem sound familiar to anyone?
If you are using a laptop, please try blowing out the dust of all the fans. If you are using a desktop PC, please try removing the side of the case, and clean out the fans inside it as well (wear an ESD band if you're going to touch the motherboard).
The wiki should have information on overheating issues as well, including a link to a program that can monitor the temperatures of your hardware.