Microsoft says if you turn off your PC without first shutting down Windows, your hard drive could become more fragmented, files could become corrupted, and you could lose data. But according to a PCWorld report, it is safe to turn off a Windows computer without doing a shut down.
We ran 30 iterations of an informal test, turning off a pair of systems running Windows XP without first shutting down Windows. Each time we left documents open in Word, Outlook, and Quicken. And we left our Internet connection up and running.Disk Doctor found no disk errors, and files were intact--at least up to the last time they were saved, but not always to the point of the last edit made. Outlook recovered without a glitch, and so did Quicken.
After we turned each PC back on, we ran Symantec's Norton Disk Doctor and the Windows disk checker to see if the hard drive had suffered any ill effects. We reopened the applications that we had left running and reconnected to the Internet.