Don't freeze or fry the box. This is commercial grade equipment, not MIL SPEC. Temperatures 20 degrees above your home or office ambient of 70 degrees F will do damage. For solid state components (the chips') temperature equals time, so that by raising the temperature you are decreasing the life. This generally doesn't make much difference, except for the CPU which is probably running at an elevated temperature already.
Hard drives will fail if you change the temperature drastically, like by attempting to operate them when the were experiencing 40 degrees or zero degrees a few hours earlier. If a hard drive is brought in from the cold, allow 24 hours of getting used to the new temperature WITHOUT TAKING IT OUT OF THE PACKING BOX. The problem here is not really temperature, but humidity, and the possiblility of condensate within the drive.
Solid state electronics can be catastrophically damaged by shock. It seems that it spurts certain molecules out of their designated locations. So don't drop chips, boards, or peripherals.
A lightning stroke nearby can produce magnetic fields large enough to move silverware. On intercepting a conducting surface, like all that copper striping on your mother board and add-on cards, the buildup and following collapse of the electric (and magnetic) field will produce an electric current in anything that conducts. This might take your computer for a digital joy ride, when all of a sudden electrical signals show up of the wrong value or polarity.
Might burn some things out too. The easiest protection is a steel case, for the electrical currents will be produced there, that is, on the surface of the case, and the field will not penetrate to your puter's motherboard. That is why MAC users turn off their computers during a storm; the older models had plastic cases.
And then the house electric also goes off, or switches over. For a PC running DOS or Windows 3.11 it really doesn't matter. Linux, MAC, Windows 95/98 will all freak out, but most will rebuild the file system on the next reboot. If this happens frequently, and annoys you, invest in a UPS box.
Sudden spikes (or drops) in the house electrical system will show up at your computer as a high frequency signal, and may get misinterpeted by the CPU. A line filter should take care of filtering these out, although most computer power supplies will do as much.