Thank you, my computer is out of warranty. Now, I have purchased warranty extension: [U4867PE] -Electronic HP Care Pack Next Business Day Hardware Support - Contratto di assistenza esteso (rinnovo) - parti e manodopera ( per solo CPU ) - 1 anno - on-site - per Workstation z600, Z620, Z640, z800, Z820, Z840.
After activating the CarePack call the service center for repair.
After write on this forum the result.
Domenico