As we upgrade our PCs, we almost never reduce the system's overall power consumption along the way. So, after a few significant component upgrades, your machine's power demands could outstrip the capabilities of the power supply that came with the computer. This is especially true for users who upgrade an older graphics board to a newer, more power-hungry board with dual power connectors. Case in point: Upgrading an Nvidia GeForce 8600 board to a GeForce GTX 295 can quadruple the power demand on the PCI-Express channel. Not surprisingly, the power supply is one of the most commonly overlooked components in the world of PC upgrades.
If you've made a few upgrades to your system, take a moment to evaluate whether your current power supply is up to the workload you're giving it. Asus has a pretty good power supply wattage calculator to help you with this assessment. You may very well discover that you've been expecting a 650-watt power supply to run a system that can draw more than 800 watts under peak load. Upgrading to a more appropriate power supply can make your system faster and with greater stability.
Routing Cables Neatly
I know how it is: Maybe you're busy, or you don't care about the aesthetics of your system's components, and you just want to finish the upgrade so you can boot the thing and play some games. But it's a mistake to leave your PC's internal cables hanging like an impenetrable cobweb in the middle of your machine.
Good heat dissipation is critical to the stability and performance of any PC, especially as you add more-powerful (and therefore more-heat-producing) components to the system. If you block the flow of air through the center of the chassis by leaving it full of jumbled cables, you're undermining the performance of your system's fans and heat sinks. Routing cables neatly increases airflow through the system and helps keep your PC cooler.
If you look inside a really sweet machine from a performance builder like Velocity Micro or Maingear, you'll find cables virtually concealed from view, routed behind the walls of the chassis, under the motherboard, and along the corners of the case, held in place by itty bitty zip ties trimmed neatly at the neck.