Try this 1
1) When you switch ON your computer, start tapping the "F8" key to
get "Windows Advanced Options"( if boot menu appears, press "Esc"
key and keep tapping the F8 key)
Select the option "Last known Good Configuration"
2) If the problem still exists then follow Step 1 and this time select "Safe
Mode". Let me know if you are able to boot into "Safe Mode ".
Also let us know the "Operating System" you are using.