And what versin of are :emotion-8:widows usig ?

Dell Diagnostics for the D2400 is a DOS program; it doesn't run in Windows, but was intended to be run from a special DOS partition that is reached by tapping F12 during startup at the Dell BIOS screen and selecting Diagnostics.

The first file entry in the Drivers and Downloads page for Diagnostics is an update to the files contained in the special DOS partition.  Downloading it and clicking on the executable should accomplish that update.  If you have no partition to update, as would be the case if you replaced the hard drive and performed a manual installation, the installation file will have nothing to update.

I haven't fully explored the remaining two files, but I know one of them simply creates a directory in the Dell\Drivers directory on your C drive and places the files there.  You can't run them from Windows, and it appears that a DOS box won't perform properly either.  At least one of the options allows you to create a CD or a set of bootable 3.5" diskettes that allow you to run the Diagnostics.

I'm afraid I don't know of a way to run this directly from your hard drive under Windows.