I am assuming that neither one is POSTing. If this is the case, then you may try resetting the CMOS, via jumper.
That should at least allow you to get to the BIOS screen. From there, make sure that your HDDs are listed. If not, open the case and check the cables. If that is all good, but it is still not there, you could try flashing the BIOS
Flashing the BIOS should ONLY be done if you know HOW to do it!!!!!! DO NOT ATTEMPT IF YOU ARE UNSURE, OR DO NOT WANT TO DAMAGE YOUR SYSTEM!!!!!!!!
If they ARE listed, but you cannot boot from them, then there are a few options. Set the CD/DVD drive as 1st boot option, and load in your Win7 DVD. Boot into it, and check to see if your HDDs are registered. If they ARE, then exit Installation and go back to the first DVD screen, and at the bottom select Repair your Computer. Allow it to check for your installs, and let it fix the MBR.