routerboard 450g problem

Hi all
I have bought a new routerboard 450g throw internet 3 weeks ago and it worked for 2 days and stopped and the following steps happen
When I powered it up the all leds on for half second then off and the beep sound after 3 second then the lan port which is connected start working normal but after about 10 seconds all leds on for half second and off then there is no response at all and the lan disconnected , the router looks like shutdown except the blue led is on all the time.
now i can not communicate with it even with winbox, i tried to do rest but no think new.
please help me …

ask your vendor/seller to replace it with the new one. it has warranty isn’t it