You can go to netgear.com/support/ and type in your model number. It'll have the support page with manuals, firmware, and install guides. Both the install guide and manual will list what each led means depending on which one is lit up. Most extenders have 4.
You can use this to troubleshoot. If it doesn't help, report back here with:
Model #:
Firmware on it:
A complete description. Not just the led is red. What you're trying to accomplish. The steps to replicate it. the steps you've tried to do to fix it.
