I found myself the answer: when I change the CPU for an unknown reason the BIOS reset the controller configuration to IDE, so the SSD was not able to boot anymore and give "the Loader disk not found" message.
Unluckily I found that after different try and so now nothing seems to work properly, expecially the addon network card does't connect and so I am not able to do nothing.
I have to solve also this problem.
So pay attention: if you start from SSD onboard controller have to be in SATA mode!