Marco,
You may need to contact Siemens Healthcare or Up-Time Solutions to get the Third Party Service key in order to allow the system to boot back into imaging mode.
Call this number: 800 888 7436 (United States #, not sure what the # in Italy is) -- listen to the message prompts, select ultrasound, and try to reach someone in service or technical support. Explain that you have a system that you are doing routine maintenance on, and needed to open the side to clean the board area as per your bosses instructions. But you need to have Third Party Service turned on to do this, and would like to get the "Feature Key" turned on.
They will probably need all of your company information, email address, phone number, name and Serial Number of the system you have. They should not charge for this service, but I cannot be 100% certain.
Universal Diagnostic Solutions