|Hard drive space is not Memory, RAM is Memory.|
D drive is probably your recovery partition, if so, do not touch it.
Temporary fix is:
Reset System Restore from the default 12% to 8% of the C drive's capacity. This will delete some of the oldest restore points and free up space on your drive.
Uninstall programs you do not use.
Clean out your browser (History, Cookies, Temp Internet Files, etc.).
Reset your browser to keep History for 2 days and delete Cookies when you close your browser.
Do a Disk Clean up (check off everything).
Turning off the indexing should have helped.
Get an external hard drive and move many files onto the drive with DVD back ups.
Get a new larger hard drive and install it as your storage hard drive (2nd drive) and off load all of your files from your C drive onto the new drive, keeping the old drive for Windows and your programs.
You have to be a little bit crazy to keep you from going insane.
---- Save Big Bird -----