Also, try the "Analyze" option in the Windows Defragmenter,
but do NOT choose "Defragment".
We've found that "Analyze" without "Defragment" helps to isolate
It's worth a try!
Also, there is an option "Check File System" under "Partition"
in the Main Menu of PartitionWizard freeware:http://www.partitionwizard.com/