Neither the user nor service manuals provide any particular clues based upon what you have described. Therefore, I must start with the typical failure. Disconnect the speakers and try again. I expect that the unit will power up normally.
You can reference the service manual here: http://www.go-gddq.com/upload/2010-02/10...
The main power amp resides inside the subwoofer. Check to see if there is a protect light on the subwoofer.
If there is a light or the unit only “works” with the subwoofer disconnected, I would suspect that one of the amp chips inside the subwoofer is defective and further investigation is required. There are 2 large black amp-packs inside the subwoofer (STK413-400 and STK413-=430). One or both of these may be defective.
Try removing the speaker connections and report the results here.
@sarah_rver is your system a JVC TH-M303?
yes it is. had it for 13 years
Sarah Hughes さんによる
@sarah_rver just to clarify, it turns on but after a few minutes it turns off. Any LED lights on or any sign of life when it turns off?