Typically, your disk always has only active partition. A Windows operating system need to be booted from the active partition, therefore, it is very important. If you have several primary partitions on a disk, you must specify one to be the boot partition. For this, you can set a partition to active, and then this will make that the partition is able to boot an OS. Besides, a disk can have only one active partition.
To set active partition
1. Select a primary partition which you want to active, and click the Advanced -> Set Active option in shortcut menu to open the related dialog.
2. By clicking OK this will add a pending operation, and the changes will be represented in the main window.
Note
Before you make a partition active, you must make sure it is formatted and contains an operating system, or contains boot.ini file or BCD file under Boot folder. Otherwise your PC will not boot from this partition!
Setting the partition as active will cause another primary partition to change to inactive.