hard drives C & D low disc space issue

hello,

/i;ve got two drives (RP_D which is is around 4BG & then C which is almost 70GB). D is showing maxed out, but I have close to 60GB of free space on my C drive. However, I keep getting "low disc space" errors, but when I follow the message to do "clean-up", it directs me to the RP_D drive & nothing I do clears space. I can't do basic funtions like printing because of no space, yet my C drive has nearly 60GB free. Everything is responding to my D drive & not recognizing the C.  Is there a reason my C drive is not being recognized as the primary drive? Is there something I need to do in the device manager or somewhere else to redirect it in some way? Sorry, I just have no clue what's going on and it's frustrating to not be able to function due to errors that say "no space on RP_D" when I've got 60GB on C.  Anyway, if you can help me understand what's going on and how to correct it, i'd apprecieate it. thanks!