IDE Hard drives not detecting

I've got 2 500GB IDE drives installed in my tower, which aren't being detected by the bios. Weirdly, if I disconnect the power to one or the other, the drive that's installed and powered is detected and works fine in OS and bios. The only time the issue comes up is if I have both drives connected, where they just remain completely unseen by the system.

I've checked and changed jumper settings, changed every concievable bios option pertaining to storage with no change whatsoever, changed to another IDE cable all with no results.

The drives are both Seagate ST3500A630A 500GB PATA, motherboard is an ASUS P6T SE. My OS drive is connected via SATA and has no problems with or without the other drives installed.

Any ideas?

 

Are you using 1 IDE strap or 2?
Each strap has 2 connectors 1 for master and 1 for slave.
You must also set the jumpers on the hard drives to correspond with the strap connections i.e the HD connected to Master must have the jumpers set to master and the HD connected to slave must have jumpers set to slave.

 

Using a single IDE cable, (this board only has 1 IDE socket). I've gone through all the possible jumper configurations, master, slave, cable select etc.