Does pressing your Windows key - two to the left of the spacebar - bring it up? If not, you may have been attacked by malware so restart the system and tap Function 8 before Windows starts to load. Select Safe Mode with Networking and see if the Start Menu behaves normally when you log in as Administrator. If it does, go to http://www.malwarebytes.org and downlaod the programme.
Install and update it - possibly twice - and run the full scan. When it completes, click Show Results and then Remove Selected. Restart into Normal mode and see if things are back to normal.