Hi, today my MacBook Pro (mid 2012) don´t startup, no lights in the charger, etc, It was completely dead. So I read some of the comments here and I decided to open it... Here is what I did:
1) I removed the battery
2) without the battery I connected the charger and immediately saw light and ripped
- - I turned off the computer and after cleaning the dust a bit
3) I put the battery back
4) I connected again, yes there was light but it did not start
5) I kept the start button depressed for 10 seconds, I released and pressed again
- - the machine returned to normal.
Hope this helps to some others.