Ya, you need to free up or procure more disk space.
First off, it won't hurt to do a "check up" on what's there now, so open My Computer, and for each of your two drives: 1) RIGHT-click the drive and select "Properties" from the pop-up. 2) Select the "Tools" tab and then the "Check Now..." button; then the "Start" button. Dismiss via "OK" button when scan COMPLETES SUCCESSFULLY. 3) If scan DID NOT COMPLETE SUCCESSFULLY AND WITHOUT ERRORS, DO THE SCAN AGAIN UNTIL IT DOES. 4) Do this for each drive.
Now that all drives are "okay" you can move on to doing cleanup.
Use suggestions given here and things like Window's Disk Cleanup (if you're sure about the stuff that it's going to delete!) that will do things like empty your Recycle Bin. You should have AT LEAST 15% FREE ON EACH DRIVE just to run Windows successfully/well. If you can't clean it up to get to 15% free or above, then it's time to consider getting a new/bigger/another drive.
Finally, once you've cleaned it up and have > 15% free space, you'll want to "defrag" it all for better performance overall. Once again, open My Computer, and for each of your two drives: 1) RIGHT-click the drive and select "Properties" from the pop-up. 2) Select the "Tools" tab and then the "Defragment Now..." button; 3) Select the "Defragment" button in the popup. 4) Dismiss the informational popup after the pass completes, and RERUN THE DEFRAG THREE MORE TIMES. (Yes, I said that.) 5) When the last pass is finished dismiss all created windows via "OK" button or upper-right-corner red X.
GL!
P.S. A computer today really needs AT LEAST 4GB of C drive space to run reasonably....