In the BIOS, go to the menu that shows the System Setup Options.
There will be a option "Drives" that will show what is attached to the SATA ports. It will either show the drive that is attached or the word "AUTO". If it says "Disabled", select them and change to "Enabled" or "Auto"
If the BIOS still doesn't show you the drive, check the connections. Also note the PSU for that model of dell is only 275w MAX so if you have added any additional expansion cards, the system may not have the juice to power it all.
Antec doesn't make PSUs and most of their PSUs are sold by other companies as well. Most of their PSUs they've had at precisely 500W are not particularly good, old group-regulated units. Though unlikely to be a problem unless you're using a GPU.