A GFCI that will not reset is not automatically broken. It may have no incoming power, or its safety mechanism may be preventing a reset.
What the RESET button can tell you
Leviton explains that its GFCIs prevent resetting when power is absent, wiring is incorrect, or the device cannot provide protection. A button that will not latch does not tell you which of those conditions exists.
Use the instructions for your exact model
Indicator colors are not a universal diagnosis. Find the manufacturer and model without removing the device, then use the matching instructions. A light being on does not, by itself, prove that the outlet is supplying power or protecting correctly.
What to check without opening anything
If conditions are dry and there are no damage signs, unplug connected equipment and read the manufacturer’s reset procedure. Note whether other outlets are also off. If the device resets but trips when a particular appliance is used, stop using that appliance until it is checked. Do not hold RESET in or bypass the GFCI.
What to tell an electrician
Record the indicator color, whether RESET stays in, any recently connected equipment, and whether this began after installation or rain. A newly installed GFCI that will not reset needs its installation checked by a qualified person. Repeated trips deserve investigation rather than repeated resets.
Keep the diagnosis separate from the symptom.
Treat line/load orientation, supply availability, downstream faults, and end-of-life behavior as distinct possibilities. Follow the device documentation and appropriate electrical safe-work practices.
Leviton: GFCI troubleshooting and indicators. General educational guidance for U.S. readers. Product instructions and local requirements control the installation. This first-edition draft has not received an independent technical review.