Set active

If you have several primary partitions, you must specify one to be the boot partition. For this, one partition can be set as active. As a rule, a disk can have only one active partition. 

If there are several primary partitions on an MBR system disk, you must specify only one partition as active for system boot, in most case, the partition should be system or boot partition. 
 
To set an active partition: 
1. Select a primary partition on MBR disk. 
2. Right-click the selected primary partition and click Set Active.   
3. Click OK. The operation will be pended until applied in Pending Operation List. Click Execute Operation when you are ready to proceed.

Tips:
◆ Before you make a partition active, you must make sure it is formatted and contains an operating system. Otherwise, your PC cannot boot from this partition!  
◆ If you set a partition as active and there is another active partition on the disk, it will be unset automatically. This might also prevent your PC from booting.