If it was previously fine in the user's site, and if it worked fine and passed all CPU/RAM/disk tests whilst sited in CH's house environment, but now promptly BSODs again on return to user's site, then I would suggest an analysis of the user's environment. Something may have been changed in the user environment.
In particular, I would suggest consideration be given to the possibility of "unclean" mains power supply fluctuations, nearby strong or high frequency radio transmissions, and proximity EMI (electro-magnetic induction). Also check that the mains has a PME (positive multiple earth).
EMI is pretty rare. I have on only one occasion come across a definite case of EMI in computing, and that was in a mainframe computer room environment, where the cause was one data-carrying cable lying on top of another, and we solved the problem by running the uppermost cable along a 3-inch high metal bridge, over the lower cable.
Also, don't overlook the possibility of a poorly mounted chip, or loose cable connection, or dry joint on the circuitboard (the bad connection may have been accidentally temporarily reconnected by moving to CH's house).