Mark a partition as active
You must be logged on as an administrator to perform these steps.
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.
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Open Computer Management by clicking the Start button 
, clicking Control Panel, clicking System and Maintenance, clicking Administrative Tools, and then double-clicking Computer Management.
If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
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In the Navigation pane, under Storage, click Disk Management.
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Right-click the primary partition that you want to make active, and then click Mark Partition as Active.
Notes
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You cannot make a logical drive or an extended partition active. Only a primary partition can be made active.
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There can be only one active partition per physical hard disk.
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If you have multiple hard disks installed on your computer, it is 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 basic input/output system (BIOS) detects is the one that will start the computer. For more in-depth information, go to the Microsoft website for IT professionals.
