1. Go to your desktop, if you are not there already.
2.When you are on the desktop, right click, and then Click properties(if you are using vista, it will be 'personalize).
3. Click screen saver...
Ending the current computing session and stopping power flow to the unit; either by pressing and holding the power button (hard shut-down), starting a shut down process via your operating system...
No, except in exceptional circumstances, such as a power failure. Ruin seems quite a strong word! Modern PCs are designed to cope with sudden power-loss - for example during a power cut, but it isn't...