Windows 7: PC reboots if someone walk by

My PC reboots if someone walks by the machine or if I touch the metal part of eSATA or USB connector(not connector contacts). It appear to have something to do with electrostatic discharge. I am using AC power connector having three pins. This never happened with my old machine.
Any suggestion for possible remedy is appreciated.

yeah seems like the computer is not grounded properly.

The mobo is electrically connected to the chassis because it is fastened to the stand-offs by screws. Do you mean this is the cause of my problem? What I am suspecting is the opposite: The mobo is not electrically connected to the chassis. But I do not see how.

The pictures as attached below show the areas of the mobo where the stand-off or the screw touches. It indicates that the ground plane of the mobo will be electrically conductive to the stand-off and thus to the chassis.

The hole is one of the eight holes to be used for ATX mobo. I reviewed what came with the mobo or the case and found no washer(metal nor insulation) in it. I assembled PC many times in the past and mobo always looked like this. I once used metal washer but never seen insulation washer to be used on mobo.
You indicates that the mobo's ground plane should not be conductive to the chassis through the stand-offs. I believe that for making the system more tolerant of electrostatic interference. But the mobo does not appear to be designed that way.

There are 10 "holes" in an ATX motherboard that fit into corresponding standoffs... each is lined as your picture above indicates. However, this metal lining is there to protect the motherboard's PCB from carelessness, not to conduct electricity.

It's possible that you may have placed a standoff behind the board where you should not have; although, since you also have an ATX case, this is very unlikely. Nevertheless, it's possible because not every case is well made.

Which brings us to my $0.02: the case may be shorting out, through no fault of your own. Just about the same thing happened to a friend of mine who decided to go cheap on his case. It was cheaper to RMA it for another model than it would have been to have it wired properly.

If the case isn't new, then I'd say to double, then triple check your wiring... because that's really the only new variable.

That is correct. Those are the mounting points of the motherboard, and they are designed that way so that when they are correctly mounted in the case (or on the motherboard tray if your case has one of those), they are all electrically connected together thereby creating a shield. It is important that they are all correctly mounted because the motherboard is designed in this way. Referring to your image, the mounting point appears at first glimpse to be electrically isolated. However, don't forget that modern motherboards are not just double-sided but that they are multi-layered, so these mounting points are also electrically connected to the inner layers. Note that not all of these points will be electrically connected to the circuitry on the motherboard as this depends on the motherboard design. Some are, some aren't.

The other holes (those without a ring of solder) are not mounting holes for the motherboard/chassis, but are for attaching the processor heatsink assembly (when located round the processor socket). Elsewhere, they will be due to the manufacturing process of the motherboard (reference points to aid alignment of the layers).

Staple Head and Fumz:
Thank you for your responses. Please misunderstand me. I am simply stating my observation which may be wrong. If so please correct me. I know there must be something wrong somewhere.
I checked by using a circuit tester the conductivity between the metal area around the mounting hole and other area on the mobo. The result is that the mounting hole area is NOT electrically isolated on the mobo or it is electrically conductive to ground plane of the mobo to which minus pin of the 24 pin power supply connector, metal enclosures of the USB connectors, the audio connectors, etc. are conductive.
It appears to me that using insulation(non-metalic) stand-offs is the only way to avoid electrical contact between the mounting holes and the chassis through the stand-offs.

maybe its the PSU itself, maybe a connection is loose inside or a wire touching another wire?

The two pictures show top and bottom side views of the same hole.