I'm running iis7 under windows 2008 R2
The "w3wp.exe" process (the iis site) use 100%+- CPU
Is there any why I can check which part of the site cause the problem ?
In IIS 7 you can open IIS Manager and Use the Worker Processes feature, in that you will see the processes and the CPu they are consuming. If you double click the worker process that is consuming 100% cpu it will show you the list of requests that are running in that precise time, including how long they have been running and in which state they are. Usually that will show you the offending page.