Why is my dell windows not booting upon turning on?

What do you see? Why do you think the hard drive is defective? You give no details.

Can you hear the hard drive spinning up? Do you hear the fan spinning? Do any lights come on and if so do how many blinks - it is a code.

Press F12 key as soon as the Dell logo appears. This will take you to the Boot Menu. look and see if you hard drive appears in the list. If it doesn’t the drive may be defective. Select it and see if it boots. If it does you are good. If not then try the suggestion below.

Performing a Start-up Repair

Try booting into the recovery environment, if possible, and then performing a start-up repair. To access the recovery environment, turn your computer on and off three times.  While booting, make sure you turn off the computer when you see the Windows logo. After the third time, Windows 10 will boot into diagnostics mode. Click Advanced options when the recovery screen appears.

1. Click Troubleshoot.
2. Click Advanced options.
3. Then, click Start-up Repair.
4. If it doesn’t work the first time try it a few more times.