First - check the BIOS settings to see if the hard disk is detected.
If not re-seat
the data and power cables on the hard drive and on the motherboard. Reboot the computer to see if it boots up. If not is the hard disk LED flashing as the computer boots up?
If not then to further check the hard disk, remove the hard disk and attach it to an USB hard drive adapter and connect it to a working computer's USB port. If this computer cannot see this as an external hard drive nor open the various folders and files then the hard disk is definitely faulty.
Install a new hard drive in your Dell and install Windows on this hard drive, together with the Dell's device drivers and your programs.
You can download the Dell's device drivers from a another computer that has Internet access.
These drivers are available from Dell WEB site, the support download page. Make sure you select your model desktop or laptop, better still, type in the Service Tag number, it is printed on the label on the bottom of the laptop and on the back or sides of a desktop. (If the Service Tag label is missing then go into the BIOS setting and on one of the BIOS pages, the Service Tag number will be displayed). This will open the page where the specific drivers for your model computer are located. Also make sure you select the Windows XP or Vista version of the drivers for your Windows operating system. Click on this link to download the drivers: -