Arduino Nano not functioning with external power supply

Good day, i have an arduino nano which i powered with a 3s 11.1V 1450 mAh LiPo. i charged the battery and it was around 12v. the arduino nano functioned without a problem for a few months with this power supply.

UNTIL recently, now when ever i connect the LiPo to gnd and Vin, the power, Tx and Rx leds flash like crazy (as if it was having something uploaded to it) and it would not run the program on it.

when i plug in the arduino nano to my pc, i can power it and it functions correctly, i can also upload new sketches.

so my question is, why do the leds flash when it has no reason to and why did it suddenly stop working? the reccomended input voltage for a nano is 7-12V where as limits are 6-20v.

any information would be greatly appreciated

First point, is your nano a genuine Arduino or a clone ?

An Arduinos onboard regulator can handle up to 20v input, the clones are rated at only 15V, so little overhead when feeding 12v.

Apart from the Nano itself, what is the current taken by other devices powered from the Nanos regulator +5v rails?

The onboad regulator at 12V input has to drop 7 volts, which at low current is not such a problem, but any increase in current means a lot more heat is produced that its difficult for a SMD regulator to disperse, so overheating itself and failing.

Have you measure the current used ?

Have you measured the Nanos +5v and the +12v inputs voltages ?