I do not know how your computer is connected to the internet network.
Wireless, or with a network cable.
And if cable, directly to the Dsl or cable modem, or with a extra router between.

Same with your dreambox.
Wireless, or with a network cable etc.

Suppose your dreambox is connected to a router, and not on the same network as your computer.
Than you are not be able to make a network connection between the two.
This may happen if both, or the dreambox is not connected to a dhcp network, and not connected on the same nework.

Also, the stop button method only works if the box is connected to a dhcp network, otherwise you may not get a ip.

Another issue could be that your dreambox has a fixed ip into the bios.
In that case connect the service usb port to your computer, and use optiflasher advanced serial mode, detect ports, and enable reset bios factory settings, press do job.

Or,
Use a serial modem program as putty.
Use this settings..
Bits per second = 115200
Data bits = 8
Parity = None
Stop bits = 1
Flow control = Xon / Xoff

Set it on receive..
Hold the front push button, and turn the dreambox on.

If all goes well, you see the bios from the box.
Go to the network settings, and check if it has a fixed ip.
Change it to Dhcp.
Or, do the reset bios option.

The dreambox network will than be normal, set to dhcp network.
Connect the dreambox to your network, and try the stop button method.
See if you get a network ip, one in the same range as your computer network.