We can try this first :

1. Press F2 key and enter the BIOS Setup, does the BIOS see the hard drive is present?

2. If you remove/disconnect the hard drive data cable (or disable the drive in the BIOS setup), does your Dell computer say,

"press F1 to retry boot, F2 for setup utility"

If the drive is detected properly, but you get only a blinking cursor, yet removing/disconnecting gives you the message in #2 it is a boot loader problem.

3. Run Diagnostics (they are built in) - When you turn on comptuer if you press CTRL + ALT + D it will say something like:

IDE Drive Diagnostics running, please wait..."

Thanks