For your scandisk and defrag problems either run it from Safe Mode or
download this program developed by
Koldbear and associates.
Joan

Get the free ScanDefrag. It is the most advanced disk maintenance
program there is. It runs Disk Cleanup, ScanDisk, and Disk
Defragmenter. It's easy to setup and use, and it can deal with
problems like "drive's contents have changed: restarting...".
Get it and read about all the options it has that you can use.
http://home.earthlink.net/~bblanton2/scandefrag/main.htm
http://www.blueorbsoft.com/scandefrag/index.html

It is not unusual to see Defrag restart a number of times.
It is , however, unusual to see ScanDisk restart.
This is why I suggest starting it at bedtime and letting it run overnight.
Please, email "The ScanDefrag Team" if you have any problems using our
program. Your problem, will be properly attended to.  And we assure you,
that every attempt will be made to resolved it..
To see how to email us, read the ScanDefrag "Readme" file, using
ScanDefrag
under the "Help" menu.