Ok.. So I've read through this post at least 5 times and tried everything you guys suggested but I still can't get mine to work. I have an HP Pavillion dv9310us. The primary drive is WD1200BEVS (120GB) with Vista. I want to add a 320GB WD3200BEVT as the secondary drive to use for storage. Here's what I've tried:
-320GB in secondary drive (no jumper). Boots to HP screen then goes black.

I thought..hmm.. according to the WD site, it should still boot to Vista even without the secondary drive formatted.. right?? Apparently not.
So I found this thread and tried everything below:
-320GB in secondary drive (w jumper). Boots to "Windows is loading files" screen but doesn't go anywhere. ONE time it went past this to the normal Vista loading screen, hung there for about 5 minutes, then went to Windows Startup Repair saying that there was an error that occurred during startup. It froze in Startup repair. Fun..

-Switched primary and secondary drive's connectors and put 320GB drive in secondary slot (both with and without jumper). Loads to HP screen. Gets to "Windows is loading files" screen but never past that.
-320GB drive in primary slot, nothing in secondary slot. Gets to screen that says no OS. I did this to make sure it wasn't an issue with the drive.
-320GB drive in primary slot, nothing in secondary slot, Win 98 in CD drive. Gets to install screen, goes through most of that, then it goes to a black screen and nothing.. (My comp came new with Vista installed so I don't have a Vista disk and I can't find my XP disk anywhere..)
-After that happened, I restarted without the 98 disk in the CD drive in the unlikely chance that maybe it installed properly. It didn't.. I then tried again with installing 98 and it did the same thing (froze on black screen after most of the install).
I really don't know what to do from here.

I even attempted calling computer repair stores in the area and they all want to charge me anywhere from $125-$200/hour to install and format the second drive. They also said they'd need it for at least 2 days before they could even start on it. I work from home and I can't be without my computer for that long. Please... any help would be much appreciated.