hi-cpu with no reason

hallo
tried to find anser with the search but couldn't find
well, I have macbook 13" for a six mouth now
(my first mac) and it was great
I usely work with "Cubase 4" and I worked on 2 program at a time
and the cpu was great, he didn't even worked hard at all
but now I have problem to hear even one project
and it's only one program working
on the cpu meter it seem very very high
but with no reason

where do I have a cpu meter on the osx
and where can I see what the cpu spent on?
(somthing like Alt+Ctrl+Del on windoes)
and if anione have an idea how to check if somthing is wrong on the computer or any kind of a software that can tell me what's wrong, that will be great

thanx