That's not an overheating issue. It is also NOT an e74, RROD, or other random issue. It's just an issue with whatever display adapter he is using. Turn off the 360, reinsert whatever AV cables you are using on both the 360 and TV end. Then turn it back on and I'm sure it will be fine. I had similar things happen to me before and that always fixed it.
Oh, and I have a new 360 Slim. I played it for 11 hours straight the day I got it and it didn't even get warm to the touch. (It was my friday CoD night) That one big side vent puts out a lot of heat, but everywhere else on the console was not warm at all so it is doing its job. Not to mention it is so dang quiet!!! Even when I installed the games (which was about the only time I used the disc drive so far) it was barely audible. Love it!
