Check BIOS to see if the hard drive is detected, also check the settings for it. To get into BIOS or diagnostics, hit f10 when you see the Dell splash screen after restart. You can use diagnostics to test the drive if it is detected.
Things to try, remove and reinsert the hard drive. Try using an external drive case if one is available. Try booting with OS restore disk if available, the drive could be good but the boot files are corrupted. Replace the hard drive and install the OS and apps.