If they both keep working now then I guess it's possible it was just dust or something. I don't think it sounds like an overheating issue.
Have a look at see if it's a Falcon CPU chipset or not, because obviously it's less likely to cause you problems with heat. Easiest way to check is look at the power supply and see if it says 175W - the Falcon ones are all 175W while the old ones are 203W. It should also say manufactured after about Sept 07 (on the back of the 360 itself).
Best thing you can do is follow the standard directions - keep it well ventilated with a lot of space round it. Vertical or horizontal doesn't seem to make any difference. Keep it out of direct sunlight. Also, try keeping the big PSU block ventilated too - it can be responsible for overheating sometimes.
Other than that it's pretty hit or miss. My first one died fairly quickly, but my second one is doing okay so far. Remember that if it RRoD's then Microsoft will replace it for free for 3 years, but they won't touch any other errors.
well, about the friend request, i got the new xbox, without account, how can i recover my account for xbox live, cuz when i register a new profile, and go to live, with my email, its allready used with a profile :s
what do i need to do
mine ****ed up and didn't have the rings. The mobo and dvd drive broke so i yay me have one of the new samsung gen3 disk drives in my gen 2 360 and a gen 3 mobo with heatsink aswell.