The Bestec ATX-300-12E is a common power source for many desktop computer systems. The equipment has a large fan that helps cool the heating unit, since the power generated by the Bestec does create heat. While using the Bestec you may run into power supply issues, which keep the computer from functioning. It is extremely important to troubleshoot the equipment; otherwise, your desktop is not going to turn on.
Check the power cord running from the electrical socket to the power port on the exterior of your computer. If the cable is loose your Bestec ATX-300-12E is not going to receive electrical current.
Power down the computer. Unplug the power cord. Open up the computer case by removing the Phillips screws that hold the case cover to the rear of the case. Once the computer is open, find the wire running from the Bestec to the motherboard. If this wire's connection is not pushed into the motherboard the computer is not going to turn on.
Clean the fan on the Bestec. If this is dirty the power supply is not going to stay cool, which results in the Bestec's overheating and the computer's shutting down. Wipe off the fan grating, then spray a few shots of compressed air into the opening to remove any dust built up on the power supply.
Check your computer's manual for the required power. The Bestec provides 300 watts of power, and if this too high or not enough for your system the computer is not going to function.
If you've completed troubleshooting the ATX-300-12E and it still doesn't turn on when the computer is plugged in, it means the internal workings have probably melted due to a power surge. This is especially likely if there's a slight burning smell coming from the computer. When this occurs you must replace the power source with a new ATX-300-12E.