Reinstalling Windows 7

I have an Inspiron 560 and could not recover or repair windows 7 (Black screen on Boot) so I chose to reinstall windows 7.  I got a Windows 7 Backup disk from Microsoft and loaded windows.  I did not know where to put it on the hard drive - there were 3 options:  a 30GB space reserved for Dell ( probably where it should have gone but would not let me), the C: drive with 9GB named Recovery which was too small and the D: drive named OS with the rest of the space.  I selected the D: partition and everything loaded fine.  Winidows 7 works and I can get to the internet..  However,  when I start loading user files, there is no memory left.  I get a message saying disk space is dangerously low.  Did I put Windows in the wrong place?  Did something change the drive designatoins?  Do I have to change applications to use the D: drive now?  Help!