Hi:
Please call HP technical support for the country you live in at the link below (Sweden, I presume).
http://www8.hp.com/us/en/contact-hp/ww-contact-us.html
Call the number listed for Business PC's.
Tell the customer services rep that you need to order a set of recovery disks for your HP Pro 3500 MT.
You will need to also provide the serial number.