[jitter] Cpu overload, trouble with my configuration? (<-noob inside)

Hi there, 

first of all, sorry but i couldn't find any answer in the faq or with the search trough the forum.

i'm feeling like an idiot, having finally installed max & jitter on my second computer, wich worked fine on my first one, because as soon as i do something, the cpu go to 100% (even something as simple as outputting a matrix to a window with a qmetro)

Max and jitter start normally and i tried patches which work just fine on my first computer so i looked for the problem but couldn"t find it. 

Here is my system:
AMD 2500 + on Windows xp sp2
last quicktime version
max 4.5.5 and jitter 1.5.2
direct x 9.0 c
graphic drivers and other drivers quite recent
microsoft .netframework sp1

I defragmented all my hard disk but it did nothing

Did i forget to install something very important which may be the cause of my cpu overload?

thank for the help, i'm totally lost^^