Hello, this is Green-Sum, the eBay seller.
First of all, we are deeply sorry for your inconvenience. We will make our best efforts to support you.
And we are the worldwide seller. So we can't reply in real time. Please understand it.
If one of the monitor is a defect, we will definitely provide you with an exchange.
Could you check the connectivity of the monitor? and try switching the main monitor with the sub-monitor?
Let us know the Small LED right-bottom side, shows Solid green, red, or Flashing green.
Please specify which one is defective. You have four different monitors in our record.
Also, we need to contact the manufacturer for the issue.
IN order to do that, you need to provide the
1) pictures of product showing the problem,
2) About the Whole box. To figure out if there are any possibilities from shock, while delivery.
3) serial number located back side of the monitor.
And we need to receive them to our email address,
(NOT E-Bay which photo size is small)
Please let us know if you have additional questions or issue. Again, sorry for your inconvenience.