Thank you for your reply, Avishek.
I tried those commands but it didn’t work, so after googling I found another solution:
dnf group install “Fedora Workstation”

I finally got a GUI environment but it is glitchy with many graphical issues. Probably the default graphical drivers aren’t good for my old ATI 9800Pro GPU (many yellow, black and white stripes on the DVI output and an unusable login screen with disaligned constrol over the VGA output). I downloaded the Catalyst from AMD website but when I execute the .run installer it tells me that the architecture is wrong (I’m on a 32bit CPU, so I installed a Fedora 22 Server x86 version). I run the OS with the kernel “acpi=off” option but I don’t know how to add other options that I used when booting from the live ISO (pnpbios=off edd=off). May be that those options make the GPU working correctly? If I change them on the fly from the GRUB ‘e’ option, the OS doesn’t start (I get a blinking cursor over a black screen).

I’ve lost too much time but I would like to make it running. Do you know how can I figure this out?

Many thanks
Pietro

If everything else is at its place and you are logging into Gnome session by typing ‘startx’ at the command line, then you can add gdm service to start automatically at boot simply as

# systemctl enable gdm.service
# systemctl restart gdm.service

Optional :: Check Status of gdm Service
# systemctl status -l gdm.service

This should help you. If not let me know the complete issue in details and error message.