Is there any damage / liquid spillage on the system?
Restart the system and press f12 key on startup - choose diagnostics. Let it run the diags and if you encounter any errors - make a note of the complete error and report the same to us. These are onboard diagnostics and they might possible pick some error if the hardware is not functional. Also, run an extended / thorough tests on the HDD and memory to check for any possible errors.
Restart the system and press f2 key on startup to enter BIOS - check if the HDD is detected in BIOS.
If the HDD is not detected in BIOS - http://dell.to/1n3X2po - enter the service tag and download the service manual and reseat the HDD and check.
If the diagnostics encounter errors with the HDD, it needs to be replaced.
If there is no warranty, then you could contact our team to get a quote for a paid service call - http://dell.to/1vnT6CQ
If the HDD is being replaced, I would suggest you to replace it with a SSD, as the rate of failure of SSD is relatively less compared to a standard HDD. However, that is your discretion.
Also, please click my DELL-username and write me a private message with the service tag and your Name for case records.