the file or directory C: is corrupt or unreadable, please run chkd

hi, i keep getting this message all the time so I asked my computer to run

chkdsk. It tells me I can't do it while the C drive is in use and that I have

to schedule it for the next time I reboot. Ok, fair enough so I do this and

chkdsk runs process 1/3 fine, process 2/3 gets to 22% complete and then

windows kicks in and I get the same message again! Help!!??