Marking a partition as active is an advanced task that should only be performed by advanced users. Marking a partition as active on a basic disk means that the computer will use the loader (an operating system tool) on that partition to start the operating system.

Warning

Don't mark a partition as active if it doesn't contain the loader for an operating system. Doing so will cause your computer to stop working.

Open Computer Management by clicking the Start button , clicking Control Panel, clicking System and Security, clicking Administrative Tools, and then double-clicking Computer Management.‌ If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
On the left, under Storage, click Disk Management.
Right-click the primary partition that you want to make active, click Mark Partition as Active, and then click Yes.

Notes

You can't make a logical drive or an extended partition active. Only a primary partition can be made active.
There can be only one active partition per physical hard disk.
If you have multiple hard disks installed on your computer, it's possible for each hard disk to have a partition set as active. However, the active partition on the first hard disk that your computer's BIOS detects is the one that will start the computer.

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