Kernel Panic

Hello there,

I have been having serious problems with my Mac Pro (Mac Os X 10.5.8 version). It regularly crashes (kernel panic) in a variety of situations (mainly when using Final Cut Pro but also with Quicktime, Safari and in other situations). I used to reboot it and it would start working again for a while. Rcently, it doesn't always reboot properly and the flashing question mark appears.

I have noticed that the question mark doesn't appear when I turn the computer off for a while and unplug it. But I'm not sure about this.

I have been told it's very difficult to understand the causes of kernel panics. But I understand there are two main options: it might be a problem with my internal HD or it might be a problem with the motherboard. Can anybody share their knowledge? Could it have something to do with the fact that I'm still running on OS 10.5.8? Or something else?

These are the characteristcs of my Mac Pro

Processor 2 x 2.8 GHZ Quad-Core Intel Xeon

Memory 6 Go 800 MHz DDR FB-DIMM

I have also added several internal HD so I have a lot of free space.

I look forward to your comments!

Best,

Sebastiano