You might encounter situation where you may not be able to boot into Windows and you might keep getting an error that Windows could not start. This could be caused by a recent change in hardware or software.
Or then again, you might not be able to install Windows, and you may get an error saying: Invalid partition.
For such cases I would like to suggest the following tips.
Most of the Startup related issues are caused by a Damaged MBR. So the first and easy step to do is to Rebuild MBR. The easy Method is using Windows 7 Startup Repair. Sometime you might need to run it 3 different times.
If the Startup Repair fails then follow the manual method follow this post to rebuild the MBR manually.
Use MiniTool Partition Wizard Bootable CD 6.0. This is an excellent tool to Mange Partition and the best thing about this tool is you get the bootable disk version.
You could Download the ISO Image and burn it to a disk, then boot using this disk. It will prompt you to choose the program and screen resolution, so select the appropriate options. Then select your primary partition and from the right hand panel select “Rebuild MBR”
Sometimes the Windows loader drive won’t be set as active and in such cases you might face issues with booting. So we need to Mark the partition as active. In order to mark the partition as active go to Partition from the Menu bar. Then go to Modify and Select “Mark as Active”.
Sometime that option might be grayed out. In such cases, you might need to Set the Partition as Primary. Then you should be able to get that option. If none of the options works then you might want to consider running Hard Drive Diagnostic to check the consistency of the drive. Follow this article on Hardware Diagnostics.
These are only a few suggested troubleshooting steps and the list is definitely not exhaustive. If you need more help, head over to TWC Forums.