SM-N900A IMEI NULL & Rebooting every 2 Min

I have this Samsung SM-N900A and its keep rebooting every 2 min and IMEI went null on it.

Phone was working fine but i was not able to unlock it through the octoplus box because of phone octoplus communication error. So i went to the service mode and Click the usb net option and since than phone shows O on the signal bar and keep restarting every 2 min.

I have also tried to put the new software and the phone is still keep restarting it.

Please help me find the solution ?:confused: