Check the jumper configuration on the drive's back.. The jumper on the HDD should be on the MA pins and the DVD-Rom on the SL pins...
If that doesn't work:
1.- Try the HD on MA and DVD on CS,
2.- Later try HD on CS and DVD on SL,
3.- Later both on CS
And if nothing helps, set both drives to MA and SL and enter the BIOS. mostly it's the DEL key, F2 or F10, but the BIOS post should indicate which key or combination to use to access the BIOS, once in the BIOS Find the IDE drives, and go to IDE detection, save the settings and exit.
Also in the BIOS find the IDE settings and see if they are enabled. And if you don't have SATA drives installed, set the SATA configuration in IDE mode.
If none of the previous works, there must be some setting in the BIOS that's not configured correctly for IDE drives to work... So install the drives with jumpers in MA and SL configuration, then access the BIOS and set it on optimum settings and exit (in the main menu).
Your Mobo make and model could help to find the owners manual that may include information on how to configure the BIOS for any type of drives to work.