MBR (short for Master Boot Record), a data structure on the first sector of disk. It contains partition table for the drive and a small amount of excusable code for the boot start. If MBR of system hard drive corrupted / damaged, Windows can fail to boot and you may get messages, such as operating system not found. If MBR of second hard drive corrupted, you may fail to access it.
Note: When Windows fails to boot, you can use AOMEI Partition Assistant to create bootable media on a working computer, insert the media into the computer, boot computer from the media and follow the steps below.
Step 1. In the main interface, right click the hard drive whose MBR is corrupted and choose Rebuild MBR.
Step 2. Choose the type for current OS (here is rebuild MBR for Windows 10) and click OK.
Step 3. Click Apply and Proceed to commit MBR repair operation.