|Kind if difficult to tell from here. I am sure it would take 4 months to get Dell to fix it.|
Common causes are bios error or glitch, poor connection to hard drive such as cables or power, motherboard flex or failing hard drive controller, failing or damaged hard drive.
You should look at bios first. See if it auto detects the hard drive.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10