Kernel panic and no reboot allowed. What next ?

Hello,

i have to apologize, i'm not very fluent in english. My MacPro 3.1 early 2008, quad-core 2.8 GHz Intel xeon started experience a permanent Kernel panic problem at boot six month ago. I tried many tips and tricks, reboot in safe mode, reboot without extensions, clean the p-RAM at startup. Nothing seemed to work and i constantly end up with a grey screen with weird white stripes on it and the kernel panic message (black background and reboot thingie).

A bit upset, as i couldn't boot, i finally erased the disk and tried a brand new install.

There, i got a message stating that i need at least 2 GHz memory to install... Wich I theorically got : 2x1 GHz DIMM DDR2. It seems only 1 GHz is taken in count

(checked on a screenshot i previously printed of my mac specifications). I then thought i found the problem and tried switch the memory cards and bars. But it still remains helpless.

I then owns a very heavy and expensive paperweight...

Can anyone help me find what's wrong and get a new install ?