How to make your pc use less power

PCs don’t have to be power hogs, but they often are. High-powered desktops with gaming-focused dedicated graphics hardware are the most thirsty for energy, but older PCs are typically less energy-efficient than modern ones.
This is a particular concern if you want to repurpose an old PC as a media center PC or home server. Depending on the price of electricity in your area, you might actually save money by buying modern, low-power-usage hardware and retiring that old hardware.

Power-Saving Tweaks

 There are a variety of power-saving tips you can use to make your current PC use less power:

Don’t Use Screensavers; Just Have Your Display Power Off: Screensavers just aren’t helpful anymore. Rather than having your PC start playing a screensaver and keep its monitor on, have it automatically put the monitor into suspend mode when you’re not using it. You can still move the mouse cursor 0r touch the keyboard and immediately get back to the desktop, but the display will use almost no power in this state.
Telling Windows to turn off the display in as few minutes as possible will also help. If you step away from your computer for a few minutes, the display will automatically power off. Set the display to an appropriate brightness level for your room — if it’s brighter than it needs to be, it’s using more power than necessary.

 Use Sleep and Hibernate: You shouldn’t just leave your computer on all the time. But you don’t have to shut it down when you step away and boot it back up and launch your applications when you need to use it again. Instead, just have your computer sleep or hibernate when you’re not using it. You can have your computer sleep or hibernate instead of shut down from the Start menu, or tell your computer to automatically sleep when you’re not using it. In sleep mode, your computer will use almost no power, and can return to your desktop with all your open programs in a second or two. In hibernation mode, your computer will use absolutely no power, but it’ll take a bit longer to get back to the desktop. Either way, you won’t lose any of your work, and you won’t have to leave your computer on.
 If you’re in the habit of leaving your computer on to perform a long-running task like a download, use software that can intelligently manage this. For example, BitTorrent clients and other file-downloading applications often have a button you can click to automatically suspend or hibernate your computer after a download finishes.

 Upgrade to an SSD: If your computer still uses an older mechanical hard drive, that drive is both slower and uses much more power than a modern, faster solid-state drive. Consider upgrading your computer to a solid-state drive to cut down on its power usage and dramatically increase overall system performance.

Other Tips: All the standard tips for increasing a laptop’s battery life apply here, too. But you won’t typically want to micromanage all these settings on a desktop PC as you would to stretch the battery life on a laptop.
Windows already does a lot of this on its own, automatically throttling your CPU to keep it at the slowest speed possible while idle and performing other power-saving tweaks, including having your computer’s hard drives sleep while idle. You can modify your power plan and power-saving settings from the Power Options control panel in Windows.
You could also unplug peripherals you don’t use much — for example, if you have a printer plugged in but use it only rarely, leave it unplugged and powered off until you need to use it

Image Credit: Brandan Wood on Flickr, Simon Wullhorst on Flickr, Intel Free Press on Flickr