Just installede the latste version - everything works fine and streaming is pefekt. The problem is that when i turn off the power and turn it on agin f.x. the next day the screen is black. And the ATV is just bliking. No access to ATV! Then i do the Boot tethred again and i works fine untill I turn off the power again!
You cannot. A tethered jailbreak means the ATv cannot boot after losing power without repeating the tethered boot. This is why untethered jailbreaks are preferred when available.
The only avoidance is to leave the ATV permanently powered. Note that putting the ATV into Sleep (standby) mode does not require a tethered boot when you wake the ATV from sleep mode so this is what most people do to avoid the constant need for the tethered boot process.