Boot in safemode

In Safe mode, you have access to only basic files and drivers (such as mouse, monitor, keyboard, mass storage, base video, default system services, and no network connections)

Windows 95/98

copied from microsoft 180902 KB artical

1. Restart your computer.
2. While your computer restarts, press and hold the CTRL key until the Windows 98 Startup menu is displayed.
   
   NOTE: If you are using the EZDrive tool, press F8 instead of CTRL.
3. Select the Safe Mode menu option from the Startup menu, and then press ENTER.

Windows 2000/XP/Vista/Windows7

copied right from microsoft 616436 KB artical

To start the computer in Safe mode, follow these steps:

1. Print these instructions before you go to step 2. They will not be available after you shut down the computer in step 2.
2. Restart your computer.
3. Use the F8 key. On a computer that is configured to start to multiple operating systems, you can press F8 when you see the Startup menu.
4. Use the arrow keys to select a Safe mode option, and then press ENTER.
   
   Note NUM LOCK functionality must be turned off for the arrow keys on the numeric keypad to work.
5. If you have a dual-boot or multiple-boot system, use the arrow keys to select the installation that you want to access, and then press ENTER.