This is normally cause by misconfigured, corrupt, missing or unreadable files. Have you installed anything significant recently? Service pack or a lot of updates? Any new Hardware? Or have you dropped the laptop?
Hopefully we can simply re-write the files that are needed to boot.
If you have a Windows 7 Disk available start the machine up and boot from it. Choose your language and press next.
At the bottom left should be an option "repair your computer."
Once the next screen loads select "Startup Repair"
Give this some time to complete, it can sometimes take up to 30mins
Once complete, restart the machine and see what happens.
If this is not successful, boot the Windows 7 disk once more and go back into "repair your computer"
This time select "Command Prompt"
Once you are in there try typing the following...
This will replace the Master Boot Record with a copy of the original version. Once this is done, type...
This will write a new boot sector on your hard drive.
Once this is done you can close the recovery console and restart the computer. Hopefully it will fix your problem! If not I would recommend running a disk check on your hard drive.