Yup thats my pc case. Finally I managed to open it by seeing the pic of the open computer in another website. Thx for ur help.
http://www.ehomeupgrade.com/media/hp_z500_...ment_center.jpg I have looked everywhere on the web and in the manuals the pc came with, and still havent found info about it. Some say that "horizontal computers" are great for space saving issues, but bad for parts replacement ones. Does anyone know how to open it, so I can clean the dust of the main fan? Thx in advance.