Backtrack 5 - hard lags

[toxinek]

Hi,
I have a problem when installing BT 5. I tried to install it from DVD (for dual boot) but when I start up Live enviroment it's so much lagging. Anyway I managed to install it and I was thought that it may be caused by the DVD (slow speed, blabla) but it wasn't. It was kind of weird because right after the gnome boot it was looking fine for like 10 secs but then the whole GUI lags. When I'm writing in terminal it's okay but when I'm trying to open something or when using the menus it's madness or moving a window (GPU not working properly?). And CPU is still loaded about 90%. I installed back BT 4 which is working fine. I'm a beginner with linux so I have no idea :/. Thanks for any help.

Installed BT 5 32bit (Gnome) and 64bit aswell, same problems, both EXT 4 (15 GB) with 2.5 GB swap.

Laptop:
Asus N51vn
C2D P8700, 2.53 GHz
nVidia GT240M 1GB
HDD - 5400

[Aspekt]

I personally don't think it's your GPU, I haven't tried running gnome, but my little Acer Aspire One aoa150 with a slower processor and integrated graphics can handle KDE4 with full desktop effects without lagging at all. Could be a different hardware problem or another case of driver incompatibility? I'm not entirely sure, just trying to eliminate one of the possibilities.