Mitel 5340 stuck on DHCP Discovery

[Redcor]

Hello to everybody,
I need help.
I had as a gift from a friend a MItel 5340.
He said to me this phone work with SIP protocol also.
But I have an issue. I switched on the phone but I can't do anything else, because the phone shows on the display
"DHCP DISCOVERY" and after, "contacting RCS" and after "RCS error"... It needen't push any button because nothing happens.
Is it the phone broken? Or ther's something I can do to make it work?
Could it depend on my modem/router depends? Fritz Box 7530?
Thank in advance .

[johnp]

Continuously hold down a volume key while powering on to get te menu. Choose no until phone mode