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Regarding the extension of partition C:, how do you get to the opinion that this could be a feature of the machine itself?
Please imagine the disk as a pile of bricks: let's say partition c: is the lower 5 bricks, partition d: is the next 20 or so bricks. You now take off the upper 10 bricks from partition d:, but there still is no room to add them to the first 5 pieces. You need to remove the remaining 10 bricks of partition d:, and then, you're able to add some bricks to c:
The windows OS can only extend a partition into free space. Other partitioning tools (either free- or payware) are capable to re-locate partition d: on the disk (i.e. moving it to the end of the disk, thereby freeing up space BETWEEN partition c: and partition d:), and can then extend partition c: