My laptop was working fine up until this morning when I woke up. The power indicator light that is normally solid green was orange. I turned on the computer and it worked as normal except that it was using battery power despite being plugged in. I was able to use the laptop until the battery died. Now the power light flashes orange when the ac adapter is plugged in, and is off when the laptop is not plugged in.
I'm pretty sure it's not a battery issue, and the ac adapter itself is brand new ( I bought it just two weeks ago) and appears completely undamaged. I know it isn't an issue with my surge protector, which is working fine for other devices. My completely un-expert, non-technical opinion is that there is an internal issue where the ac adapter connects to the laptop.
1) Test output with volt/ohm meter. Be sure you are reading using a digital volt / ohm meter set for the 20v DC range. The test leads should contact the inner and outside surfaces of the barrel connect and not the center pin itself. If 20v is shown, move on. If no voltage or much less than 20v, the adapter may be bad. A -20v result means the test leads are reversed, but it is OK. See this related KB article for more help on this test.
2) Check to see if the DC in port at all loose? If the adapter plug is inserted and you gently wiggle the connection, does the AC or line or charging LEDs light up? If the DC in port is loose / damaged, it can easily be ordered as a FRU part - check the HMM or hardware maintenance manual or service part list for this model on the Lenovo support site.
If you feel able to disassemble laptop yourself, it is possible to check it out. If not, find a competent computer repair person. The jack has a cable, so is not a major problem to replace, unlike some that are soldered to motherboard.