A second HDD doesn't work.

I bought an additional 1Tb hard drive for my computer. For the first two days it worked fine, but then the computer refused to boot, it didn't even go to BIOS, just a black screen when starting the computer. The HDD works fine on other computers, and I get past the problem by clearing CMOS memory by moving the mobo jumper cap from pins 1&2 to pins 2&3 and then back before starting the computer, but I can't restart the computer or it won't boot again. So I've narrowed it down to probably being a problem with the mobo. I've tried using different SATA ports, different power ports, different cables, running with just the new HDD, all with the same results, black screen. The computer boots fine when the second hard drive isn't plugged in. The HDD doesn't show in boot order list, and HDD jumper doesn't have to be set for Vista. The HDD is a Western Digital Caviar Green 1Tb, motherboard is Asus P5Q SE and OS is Windows Vista 32-bit.