Rb750GL Disconnections

Hi again guys,

i have problems with a RB750GL. I connect the RB and works fine about 3 minutes, them Ethernet1-gateway down.
I have upgraded to new version firmware, and have the same problem.
wan => 192.168.0.X
Lan => 192.168.3.X
routes ok
Pool ok

but has the same problem, if i reset configuration and let the default configuration with 192.168.88.1 , nothing, works fine about 3minutes and then eth1 down . . . . . . .

Anyone cuold say me the problem.
i have the RB connected by jack electricity, now i wil test with PoE, . . . .

Thanks to all , and have a nice week

2 hours later . . .

I have tried with PoE, and works fine until 5-10 minutes, them ether1=gateway down…

Anyone that help me, thanks all