Welcome to Windows Seven Forums.
You really haven't given us much to work with so in the absence of any meaningful information I'm going to suggest you carry out a repair install of Windows 7.
http://www.sevenforums.com/tutorials/3413-repair-install.html
In the meantime, the following information would be useful:
Who is your computer manufacturer?
Do you have a Windows DVD?
If not, do you have a set of recovery discs?
Can you remember doing anything different before the problem occurred?
Have you installed any new software recently?
Had the computer been switched off for any length of time prior to you seeing this message?
What are your computer specifications?
Can you boot into Safe Mode?
If so, have you carried out a virus scan?
