hello there and thanx for your guide..
heres what i did:

1)In terminal i typed:
rm -rf /system/library/extensions/NV*
rm -rf /system/library/extensions/Ge*
rm -rf /system/library/extensions/Natit*
so as to remove all Intel and ATI video drivers as you said.

2)I installed downloaded kexts using Uinstaller

3)In terminal i typed:
cd /System/Library
rm -Rf Extensions.mkext
so as to delete Extensions.mkext as you said.

i rebooted with -f
and it stucks at the grey screen with the apple logo.
It is loading for some time and then everything freezes.
Same happens when i try to boot in safe mode.


What should i do? any suggestions????