I got that reboot loop if I didn't set my memory up correct in my DQ6. I would then reset CMOS and setup with one stick. In fact, I've had this with all 4 P35/X38 boards I have owned. I imagine it's the bootstrap.
My X38-DQ6 died today in the middle of critical work, the memory controller went nuts, memory usage jumped from 5gbish to 8gb, PC slowed down and everything froze. It would then hang on post at the memory size line with any memory, other CPUs I have, CMOS reset etc. It did get past POST one time but memory errors all over the shop yet the RAM passed okay on one of my other machines. The 8gb strain probably killed the MCH, even though it was always cool.
Went out and got a Maximus Formula (local place had no X48s and had no time to wait as I had a lot of work to do) and all is fine now. Didn't need to reinstall Windows, just plugged 'n' played!