Intel Mac :: Firewire 400 Camera Doesn't Work With 800 Port?

I have a firewire 400 camera that i'm using for a project and one firewire 800 slot on my iMac (Late 2009). When I plug the camera in, nothing responds no matter what I do - tried resetting the PRAM and SMC. Compare this to my older iMac (Late 2007) which has both firewire 800 and 400 ports. I plug it in and it pops up using the underlying Quicktime controller api on either the 800 or 400 port no problem. So I figured after trying to install a firewire camera library (libdc1394) which I need for my project which didn't work, that it must be a hardware issue, so I took it to the Apple store. The genius at the store booted the OS (Lion) from a firewire drive via 400 to 800 cable (no external power to the f/w drive was used) and then using the spare 400 slot on the hard drive, he plugged (daisy chaining) in my camera and it loaded! So this suggested 2 things - my OS is corrupt or my card can't read straight from my device but why a hard drive in between would change this is beyond me. I came home and installed OS X on to an external USB hard drive and loaded up from it - so this is a fresh version of Lion, there should be no software issues. Plug the camera in to the I/O board of the iMac but load the OS from the external USB hard drive - nothing happens, the profiler doesn't detect anything at all. On a side note, I installed XP and Ubuntu Linux and they also can't detect it, which further suggests its the device or I/O board when interfacing directly with this camera. I've tried providing the devices with external power, daisy chaining 2 cameras, using a usb hub....nothing works. Just for good measure, I tried to boot Lion off the external USB on my older iMac and again, it worked no problem, which to me really narrows it down to the hardware. 

I feel like perhaps the port is a bit dodgy and when the genius daisy chained it, it worked better, but no idea why. Someone said I should get a firewire 400 to usb adaptor