To restart in Safe Mode on a computer running only Windows 7, press and hold the F8 key before the Windows logo appears during booting. If your computer runs multiple operating systems, first select Windows 7, and then press F8. In the Advanced Boot Options screen that appears, navigate to the safe mode option you want, and then press Enter to access it. If you get a stuck key message whenever you press and hold F8, tap it continuously instead.
You can also make the necessary settings for accessing Safe Mode from a normal Windows session. To do so, first press the Windows key and R together to open the Run window, type "msconfig" in the Open field, and click OK. In the System Configuration window that appears, click on the Boot tab, navigate to the Boot Options section, and check the box for Safe Mode. Check Minimal under the Safe Mode options, click Apply, click OK, and then restart your computer. With this method, however, you must access the System Configuration options from within Safe Mode and select Normal Startup to boot back into Windows 7 in the normal mode.
Before restarting your computer, ensure you're removed all external devices such as CDs, DVDs and floppy disks.