Golden Rule:

Always check the power supply/UPS is set to the right voltage!!!

Found this one out the hard way myself many times, due to having a lot of U.S.A.F. bases in the area. The amount of power supplies the stores I have worked in, have had to replace due to this happening when the customer has bought their machines in, I lost count of a long time ago!!! In the end I placed printed out signs on every work bench warning to check the PSU before plugging in for correct voltage.

Must admit it sure wakes you up when it happens!!!