If...
- IDE enabled in BIOS
- Autodetect enabled in ATA menu
- Drive set properly to Master/Slave/Cable Select
- If drive is Master then the drive is connected to the end of the cable
- If drive is Slave then the drive is connected to the middle of the cable
- Molex connected - other side of the cord disappears in the PSU housing 🙂
- HDD is not kaput
- HDD is not in mobile rack
- HDD is in mobile rack and mobile rack isn't kaput
... then it should work.
Edit: wait a second, so you have a SATA or a PATA HDD? The title said it's a SATA while and post says otherwise.
Make sure power is connected (if it has both the SATA power connector and the molex make sure you connect only one of them), SATA cable is connected, SATA controller enabled in BIOS, PCI bus is not overclocked, boot order set properly