Use a program called TreeSize to determine where exactly the space is being utilized on C:. Unless you are skilled in reinstalling the OS from an installation DVD, leave the D: drive alone.
The C drive contains 136GB of total space.  A total of 108GB are being utilize (116GB - 8GB from the desk top) leaving 20GB free. The D drive contains 10GB of total space. 5GB are being utilize leaving 5GB free. Question: How can I find what files are needed and what are not. I would like to delete the files that are not needed in order to free up more space. Thanks
Freeing up more space: Problems with files from the C and D drives