Buy canned air at any computer supply store and pop the top of your PC and blow out the dust once or twice a year. Pay special attention to the power supply area and fan. Excessive dust build up will cause your computer to operate hotter and reduce it's useful life span. Power Power brown outs and surges can be prevented by purchasing a UPS system. Be sure to get at least a 250 Watt model and do NOT plug anything into it other than your computer, monitor and modem.
Some models have protection for modem lines.
This is a very good feature to have since most lightning damage to computers enters via the phone line. A UPS will give you a more stable system that isn't interupted by the frequent power blips that we have. They make sure that the computer is reliably recording information to the hard drive. Most of the system software problems come from corruption of the operating system through time and use. Running these applications makes sure that the computer knows exactly where it has recorded your data to the hard drive.