Many people have problems running ScanDisk and/or Defrag, with the program running 10% or 30% and then stalling. Often with a message that Windows is trying to write to the drive. To run ScanDisk/Defrag successfully:
Go to Start > Run and type msconfig in the Open: box
On the General tab, uncheck all items listed under Selective startup (make sure that Selective startup is selected)
Hit apply and OK and restart Windows
This starts Windows with only the basics running; Insures nothing will interfere with ScanDisk and Defrag
Run ScanDisk and Defrag, when ready go into msconfig and select Normal startup and restart Windows