CST 2011 on windows 7 goes very slowly, where is the problem?

I have a problem, on my new computer where I have CST 2011 and my windows is 7. I had nearly no problem with my simulations on vista and CST2010 but now they do converge very slowly on the new computer. dose anybody have an experience with this version of CST?
my processor is AMD dual core with 4G RAM.
any suggestion?