If you've added a lot of new components to your PC, you may be overtaxing your existing power supply, so look at getting a bigger, better one. Power supplies can cause problems -including random crashes or even component failure- if they are asked to prduce more power than they are designed to generate.
Most power supplies are rated according to their maximum output(in watts). Online tools such as PC Power and Cooling's Power Supply Selector can provide a quick ballpark estimate of the wattage you need, based on the components in your system. To calculate your wattage requirements more precisely, use the table at right to tally the power drawn by all your components; then tack at least 30 percent more for headroom and the upgrades that you'll add over time.