"-Nmedia 500-watt Silent PSU"
You can try to get it to boot from another disk like an OS install disk if its not recognizing the HDD (i'm assuming the HDD is recently formatted and blank). Or like said above plug the HDD into another computer and reformat it as one partition NTFS (if using XP) or FAT32 (Linux). Then plug it all back in and if BIOS comes up great if not then its another problem.
Also, if you have a spare drive around try the same with that and see if both drives do the same thing its likely not the HDD problem. then its specific device troubleshooting.
Break the system down to just the necessities, and leave out the graphics card, etc for now.
And a real simple check, make sure the HDD is well physically, as in all the pins are straight if using EIDE (Its rare but I've seen it before) and I dont know much that can go wrong physically with a SATA plug.
Hope all this works out for you.
Impulse