airport extreme - why is the light blinking

yes, there was a message that the unit may be overheating - but its not overheating and is in a cool, well ventilated location. not sure if the software update could be an issue. the light was initially green, but started to blink after the software update and a timer was set up for the power strip on which the router and iMac are on.

It was pre-owned, factory reset ‘tower’ type unit. It powered up, had a solid green light. I called Apple to have a tech help set it up. He said it needed a software update, so I did the update. But through the rest of the set up, the amber light was blinking, the message on the airport utility said the unit may be overheating. The tech said the unit was probably overheating (I took his word for it, though it wasn’t hot) and that I wouldn’t be able to use the unit since it was out of warranty, etc. In the meanwhile, I got another router, used it for a while. I still wanted to figure out if the airport router could work for me, so I called and spoke with a second Apple tech. I explained how I had not been able to figure out the ‘may be overheating’ notice. He walked me through the set-up, upon set up, the light on the unit was green. He seemed to think from his resource that the blinking light was due to a previous ‘incomplete setup’. So, I thanked him, thought nothing more of the issue until a few days later, when I placed an outlet timer on the power strip. The internet was working fine, but on the second day I noticed the blinking amber light on the airport router… so it could be a coincidence or recurrence of the initial issue: that the utility claims possible overheat when there is none… or a software update glitch… ?

Thank you for the info for the ‘enable file sharing’. I did as you suggested up to the point where I was supposed to wait 10 seconds and then reselect ‘enable file sharing’ and then select update. Yes, it worked - that is, the blinking amber light on the AirPort Extreme turned green once the reset was done. (Actually, I believe I may have de-selected ‘enable file sharing’ and updated without reselecting ‘enable file sharing’ the first time by accident, which also resulted in a successful reset yielding the green light). Since that time, I have not used the timer on my power strip for the sake of convenience. However, we had a power outage in our area after which the unit came back on, predictably, with the blinking amber light and the Utility menu suggesting that ‘the unit may be overheating’, which I then knew how to reset. Thank you again - it seemed like a random unrelated message ‘unit may be overheating’ to be corrected by re-selecting ‘enable file sharing’ - any reason that you know of that this reset is needed?