I was remodeling my den and the pc was disconnected and moved not to get dirt inside it. While I had it out I cleaned it out with compressed air and modified the side window and rear of the case to fit 120mm fans. The only thing I did during that was removed the fans from the fan controller and unplugged the dvdrw cables to have better access to the fan controller. I fire it up, it runs fine, 30 minutes later, just shuts off, instantly. Press the power button, goes on for a couple seconds and again shuts off. I opened it up cleared cmos, loaded my settings and it has been going fine so far for maybe 20 minutes. I have everything that would turn the pc off cause of too high temps turned off as it never gets anywhere near those temps. So, if it comes back, what could it be? PSU is stable as a rock.