Help please! Power voltage switch on pc had moved (don't ask, kids! arrgh), anyway, pc made a loud bang and smoke came from power unit but the thing which is weird, the pc is fully functional so what has happened? If any one can help I would be very appreciative.
What is the voltage in your area? Are you on 115 V like most of North America or are you on 230 V? If you are on 230 V and switched it to 115 V it engages a voltage doubler circuit which would have gotten cooked real quick, and often damages the primary side in the process. If you are on 115 V often times it just wont boot, but the loud sound indicates something blew, and you dont know what. Obviously it wasn't something major on the input side but it may have resulted in extremely high ripple on the output which can damage everything else in your system.
Power supplies are impossible for the average user to identify what went wrong, most people dont have the necessary tools. If it made a noise trade it out for a new one ASAP, preferably one with active PFC this time so it doesn't have a voltage selector switch.