Once the primary partition is created you must make an active partition to tell DOS that the operating system resides on this drive or you can also make any logical drive as an active partition. It is a must to create an active partition otherwise DOS will not know where the operating system files are. Normally Primary DOS partition is the active partition. 
Steps to create the active partition are as follows:
Firstly run the FDISK utility.
Select option 1, create a primary DOS or logical drive.
On the second screen select option 2, create active partition.
After this the FDISK will display all the partitions and you select the primary partition to make it active (you will see the letter A in front of the drive telling you that this is the active drive in the computer).
Exit FDISK.
