Well, this is what was happening to my original 360 a little before the rrod showed up. It might be your xbox telling it that it's dying. :/
Might be time for you to look into a new one, sadly. At least you were a lucky one. Like me, your original xbox lasted a lot longer than the average for them. Got my first 360 around launch, didn't have to get a new one until August of last year.