Boot the Windows 7 DVD Repair console or Repair CD, accept any offered Repair. If it won't start, boot back in and click through to Recovery Tools list to run Startup Repair up to 3 separate times until it starts.
If it still won't start, make sure Windows 7 is marked Active using DISKPART from the DVD/CD Command Line: Partition - Mark as Active
then run Startup Repair again x3.
On the possibility that the OS is unbootable due to infection, try booting, updating and then running one of the bootable AV scans: http://www.techmixer.com/free-bootab...download-list/
If it cleans up an infection, try Startup Repair again x3.
If this won't work, you can copy out your files using this method: Copy & Paste - in Windows Recovery Console
Then find an installer for your licensed version and clean reinstall after wiping the HD to overwrite any possibly infected code: SSD / HDD : Optimize for Windows Reinstallation