All of this, of course, assumes that the systems are working correctly. When I first installed Vista on my PC, I configured it to go to sleep after 30 minutes, but it has been unreliable. Sometimes it fails to go to sleep, and at other times it fails to wake up. Sometimes I experience the worst of both worlds: the drives and fan are spinning, but the monitor is blank, and I cannot get the machine to come back to life without powering it down and turning it back on.

Image Credit... Bruce MacPherson

I spent numerous hours trying to fix the problem, including updating the BIOS, installing up-to-date versions of all my device drivers, checking to make sure there were no unnecessary applications running in the background and, of course, scanning for spyware and viruses. The results were encouraging. After all that fiddling, the machine went to sleep most nights and woke up most — but not all —mornings.

I then installed Co2 Saver (co2saver.snap.com), a free program for Windows XP and Vista that seems to have solved the problem. It gives you a simple control panel to specify when to turn off monitors and disk drives and put the machine to sleep. It also adjusts some hard-to-configure settings. One option forces the machine to “Initiate sleep mode if system doesn’t sleep automatically.” This feature, according to its developer, Lee Hasiuk, defeats Windows attempts to keep a machine awake if it thinks (correctly or otherwise) that it is detecting a background task other than mouse or keyboard activity. Now my machine sleeps and wakes properly almost all the time.

Whatever machine you’re using, consider having it go into sleep, standby or hibernate after about a half-hour of inactivity. The shorter the period, the more energy you save. Graphic-intense screen savers can actually waste power.

Unplug unused external power supplies because they can draw energy even when they’re not connected to a device.

If you’re shopping for a new PC, be sure that it meets Energy Star requirements, ideally the ones that go into effect July 20. The new standards require that 80 percent of the power consumed is actually used by the PC.

Use an L.C.D. screen instead of an old-fashioned cathode ray tube monitor. L.C.D.’s are as much as 66 percent more efficient than C.R.T.’s, according to the Energy Department.