I recently created a second partition on my C: Drive. I changed my mind about installing a new OS, so now I'd like to delete the partition and merge it back into one C: Drive. I've already had to mark the partition as inactive, and now I'm ready to delete it. But when I try to delete or format the partition I get this message:

Delete is not allowed on the current boot, system, pagefile, crashdump or hibernation volume.

I understand that this message should come up if I was on the C: Drive partition, but not on the second partition I created. How do I delete this partition?

Press Windows key + X
Click Disk Management
Right click it, click 'Format'
You will receive a Warning dialog, click OK to continue.
The next step is to select your file system option, in this case, go with the default which is NTFS.
The formatting process will now begin.
Once complete, the drive will be displayed as a ‘Logical Drive’ in Disk Management.
Right click the ‘Logical Drive’ in Disk Management, on the contextual menu, click the ‘Delete Volume’ option. Click ‘Yes’ when the warning dialog appears.
The Volume you deleted will now appear as ‘Free space’, you will also notice that the disk icon no longer appears in the list of volumes.
Right click the Free space partition, and click Delete, click Yes on the Disk Management warning that appears.
　 The volume will now appear as Unallocated Our next step is to merge back that unallocated free space with the system partition. Right click the System volume and click the ‘Extend Volume’ option on the contextual menu, click ‘Yes’ when the warning appears.
A wizard will now begin that will guide through the steps to merge back the unallocated space with your system partition.
The wizard provides a simple procedure to merge back the unallocated space with the system drive. Once you have selected the space, click Next, at the end of the wizard, you will see the amount allocated.