What did you use to reallocate space from D:? Are you just using Windows Disk Management? If so, the problem with that is you'll have no access to the system drive since that's the drive you're booted to. So there's no way you'll be able to extend that free space to your C:. You'll have to boot to something outside of the OS you're using.
You can use a program like Partition Magic, which will do what you're wanting. But you've got to pay for it.
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