When working on your PC or any mains-powered equipment, always disconnect it completely from the mains wall socket.

Never dismantle the actual PSU in your PC. This unit contains potentially lethal mains voltages, even when it is disconnected from the supply. They are not user-repairable. If it fails, replace it with a new one.

Beware of sharp edges inside PC Cases and the small solder pins on boards. A harmless-looking case edge can be as sharp as a razor, and remove large chunks of flesh if accidentally nudged with a slipping hand.

Always remember to completely disconnect the power before connecting/disconnecting components or cables.

When making cabling connections of any kind, use firm, even pressure but never excessive force. Small signal pins are very easily damaged if connected incorrectly. If it just won't fit, try to establish a reason rather than giving it a 'hopeful' shove. Most connectors have some kind of alignment system to prevent incorrect connection.

PC devices/peripherals are generally very delicate in nature. Handle them with extreme care and always employ some method to disperse static electricity. A good trick here is to keep in mind how much it costs to replace when you take it out of the packaging!

With the exception of the exterior of the case, never try to clean any part of your system with any liquid detergents or cloths.

If you find a build-up of dust inside the machine after some time, disconnect the unit completely, remove the case sides and use an Air Duster to blow out the dust from the case. Air Duster should be available from most electronic supply shops, and is basically a can of clean, compressed air.

The key to working with PC's is to stay calm, check your work over and over again, and if it still doesn't work, ask someone who knows.