I removed all screws, but IT WONT FUCKING BUDGE!
Idk, my dad would help you, he is an electrical engineer, but sadly i live far away from you so that would be impossible 
Have you perhaps tried hitting the side panel 2 or 3 times?
That looks like a SCALEO machine. I have a SCALEO P from 2004 (As shown in the crude doodle). My SCALEO at least doesn’t have a side panel, but instead has a “unibody” panel that covers the top and both sides, and from what i could tell, yours seems to have the same. How i got mine open was to first unscrew (which you’ve done), and then push the metal housing back, and lift. Some force may be needed when pushing. Removing the face panel may also help. Be sure to do things safely, and look for the official documentation for your machine.
Mine is a Scaleo Pa 2666 / P2
UPDATE: Reseated the GPU, etc.
I found out that there is WLM on the machine! And Windows XP!