Cannot Scan/Defrag Local disc

Hello,

i been trying to defrag my local disc but everytime i started to defrag, an error messages appear saying:

a). Disk defraggmenter has detected that Chkdsk is scheduled to run on the volume..

b). Window was unable to complete the disk check..(when i performed Error Checking on my local disk)

What is wrong with my computer and what should i do with this?

Millions of thanks..