Why does my laptop not boot

This problem could be caused by a failing hard drive, you can run the built in Dell Diagnostics by pressing F10 and select diagnostics. If the drive passes diagnostics then you will need to run Windows Recovery, either from CD disk or download from Microsoft.com. Run Windows Recovery and see if it can repair the boot and system files. If it is not able to repair then you may have to reinstall Windows. If the drive does not pass diagnostics then it should be replaced and install Windows on the new drive.

If the hard drive is failing, further attempts to repair it may cause the data to be inaccessible. In this case, wait until you have installed Windows on another drive and then try connecting the old hard drive using an external drive case with USB to your computer to see if it can find and transfer data from it.