How To Solve “Access Denied” error on Drive D On Windows Pc

I run Windows 7 ultimate on my Lenove G580 notebook system bit 32, HDD 500GB, RAM 2GB. On certain occassions I do get this "access denied.You don't have access privileges to this drive" whenever I try to access my drive D.
Sometimes, I can go for days without encountering such an error message but when it happens, I am always forced to restart my computer so that I can have a successful access to my Drive D. What could this error signify because sometimes it is so irritating that I have to reboot my system even if I had something urgent to access from the drive…please assist..
