There may be something running in the background that's conflicting with both ScanDisk and Defragmenter.
Go to Start/Run, type msconfig, click the Startup tab, write down all of the items with checked boxes, uncheck all of the boxes except ScanRegistry and System Tray, click OK, restart the computer, and run ScanDisk and Defrag.
If that does not work, then run them in Safe mode.
After running them, go back to the Startup tab, recheck each item that had a check mark, and restart.
For the slow overall performance of your system, uninstall all unused programs from Add/Remove Programs in Control Panel, delete all files from the Temp and Temporary Internet Files folders in the Windows folder, update your AV program and remove all viruses, run Ad-aware and Spybot to remove any spyware, and prevent any unnecessary programs from running in the background by unchecking them in the above mentioned Startup tab.
If it still runs slow, then check if your virtual memory is activating. If it is, then your system needs more RAM.