Starting Windows 7 in Safe Mode is an excellent next step when starting Windows normally is not possible. Safe Mode only starts the most important Windows 7 processes so, depending on the problem you're having, you might be able to troubleshoot or even fix the problem from here.
To begin entering Windows 7 Safe Mode, turn on or restart your PC.
Just before the Windows 7 splash screen shown above appears, press the F8 key to enter Advanced Boot Options.
Not a Windows 7 User?
See How Do I Start Windows in Safe Mode? for specific instructions for your version of Windows.