you'll need to boot into safe mode to run scandisk or defrag,
To boot into safe mode:
1. Click Start, and then click Shut Down.
2. Click Restart, click OK, and then press and hold the CTRL key until the Microsoft Windows Startup Menu appears.
On some computers, you can use F8 instead of CTRL to bring up the Microsoft Windows Startup Menu.
3. Enter the number for Safe mode, and then press ENTER.
you should be able to run scandisk/defreag OK now