I ran into the same exact problem w/ the same MOBO as you. I was designing a "bench power system" so I can run my car-pc on a workbench in my house. I used an older power supply... (by the way my system has ITPS + 80w power supply also)
Made a switch that acted as the ignition switch, the system came on perfectly the first time... Booted to windows and everything... shut the machine down, resarted then I got the 20 or 30 seconds and random restart.
I racked my brain a bit, checked the HDD connection which was loose. Fixed that, but still had the same problem. Racked my brain over the weekend, went into BIOS (checked what the MOBO was reading for voltage, it said 9.2v @ the 12v line... DOH! it was obviously my power line comming into the machine, updated the BIOS and set up the new "Vehicle power test system" (using another ATX power supply)
Let me say a few things before I close, I didn't have a voltage meter during all this (left it @ work) This problem would have been solved easily with that tool... Also this is my bench test system, I had to emulate a vehicle's power system 12v (with ignition signal) I did this by taking an ATX power supply from a normal computer out... I tapped off or jumpered off the green and black wires on the ATX connector. (This tricks the supply into turning itself on whever it has wall power) Then I tapped into two yellow wires (12v) one has a on/off switch the other was steady 12v... I then connected this to my car-pc's ITPS.
To turn my system on, I make sure my ATX power supply is running then simply slip the switch and poof.. my car Pc thinks its in the car !
I honestly would check the power comming into the machine, boot the machine and see what the MOBO is reading for power on the 12V line. Also Update the BIOS too while your playing with things... make sure you download the VGA drivers too (you have to update both at the same time even though your not messing with VGA yet)
Test what the ITPS is giving to your machine for voltage... You know it seems like that little guy's "regulation" actually under powers the machine.. even though my ystem was up and running the 12v line reads as getting 10.4 (which is kinda low, below atx standards)