Do you get any BIOS info when it boots?
If the hard drive makes a steady click; the hard drive is probably bad.
Can you put in a bootable OS disk and see if it will boot from a disk instead of the hard drive? you may need to select the boot menu which is F12 I think on the Dells and tell the system to boot from CD. OR change the boot list in the BIOS.
My "guess" is bad hard drive.