Sorry for not getting back earlier, just spent 3 weeks holiday abroad.
I've emailed rockstar like y'all said. No response. Yes I have the DVD version.
In the meantime my neighbour reinstalled my PC with Windows Vista 64 bits edition.
DirectX 10 and newest video card drivers.
I've installed the game.. run it... and now it's even worse than before, the game crashes with the intro movie, starting a game takes even longer than my previous computer. I just get kicked back to windows.
So only two options remain.. Windows Vista 32 bit edition and/ or calling Rockstar Support.
And thinking that i've already finished the single player on my old PC before... but that took a lot of sweat and anger because it always crashed...