Actually, they don't know what the exact reason, so their technician cannot repair the DVR. It might caused by user damage, misuse or external causes.
If what you said was true, the result is that the dvr get damaged after you used 4+ months. We need to refund you!
However, we are unable to do a full refund or give a replacement as per your request. Please read our warranty and return policy!
The warranty starts from the day when you received the dvr, and your order number shows that you received it since April 12, 2016.
We only can do a do a partial refund, because you used the dvr for 4+ months. Only within 45 days of receiving the item can get full refund and you need to send back the the item to us. Return shipping reimbursement is not available for this
According to your case, the best solution is the partial refund.