If you cannot boot into Windows normally and have tried other troubleshooting steps, there are a few other options.
Safe mode. Try booting into safe mode with networking, then if that doesn't work, try without. Safe mode uses basic drivers and is generally good for narrowing down an issue. If the issue still persists, could be dead components/bad drivers
Bad drivers. Try to narrow down what components (if any) could be causing a driver issue (in particular GPU).
As VioDuskar said, dead/bad components can cause an OS to not load. Check these. Reseat RAM, CPU, GPU, check hard drives, etc.
The fact that Windows couldn't find a problem with the boot sector is a good sign, but it doesn't help us very much. Try repairing from a Windows boot medium (Windows install DVD, flash drive, etc.) This may find a problem. Never hurts to try.
Manually reformatting a boot sector/Windows partition can help if you know what you are doing. There are many guides online for this, just BE CAREFUL. This can cause more problems than it solves. If you're uncomfortable with it, don't do it! Data could be lost.
Restore points/backups. If all else fails, revert back in time to a last know configuration. A Windows ISO/recovery disk is also an option.
If you can't do this (don't have any backups/restore points), move all of your data off of the OS with a live Linux USB. Then try reinstalling Windows. Again, last ditch option.
Remember, your data come first, Windows second. Backups from a Linux USB can never hurt and may allow you to reinstall Windows and get back up to speed quickly if need be. I hope something here helped. Good luck!
