@benben2004 

Hi,welcome to our community.

Did you ever try different power sockets for the range extender?

How far did you put the range extender from your main router? 

Did the problem immediately happen since installation?

You may put the range extender near main router, reset the extender and reconfigrue it again.

If the LED still shows abnormal, it is suggested to contact retailer or local support to confirm warranty.

Thank you and best regards.