XP Can’t access D:

Running XP prof with SP1. I ran defrag last night and now I can not access the D: . I can access the folders if I know the name, and can go thru history to files on the d: . (and the OS is operating from the D: . If I try to access it from run on the start menu I get the same problem. task manager says not responding. I can copy the files to another HDD but the main HDD is 20 gigs and the second has only 3 gigs left. I ran chkdsk but no difference. Any Ideas? Thanks in advance.