If you are running Windows 98/ME/XP, go to Start/Run
In the Open box, type "msconfig" without the quotes, then press Enter.
That will start the System Configuration Utility,
When the System Configuration Utility comes up.
Click on the General tab.
Under the Selective Startup Section, click on the box next to "Load Startup Items." That will remove the checkmark.
Click on the Apply button and allow the machine to reboot.
Do your ScanDisk and Defragmentation.
Reopen the System Configuration Utility.
Click on the box next to "Load Startup Items." That will put the checkmark back.
Reboot.

If you are running Windows 95 move all Shortcuts out of the Startup Folder to another folder.

Reboot. Run ScanDisk and Defrag.

Move Shortcuts back to Startup Folder.

Reboot.