The main culprit behind getting the Windows failed to startup error is recently installed Windows update. So check if you have installed the latest Windows updates and uninstall it.
But if this is not the case then try performing a Startup repair. Follow the steps to do so:
- Insert a Windows installation disc or Windows system repair disc in the system.
- Restart system > boot from the disc.
- Choose language and other preferences > click Next.
- Now a screen displays having Install Now button at its center
- Click on Repair your computer in the bottom left corner.
- And as the whole process is completed > restart your system.
Note: if you are using the system repair disc, then you will be taken to next step. Choose operating system you want to repair > click Startup Repair and follow the onscreen instruction > restart your system.
Hope this works for you.