Battery wont charge, and doesnt work off magsafe power.

Hey guys, I have a 2011 13 inch macbook pro that only turns on if it has a battery with power in it. Here are further details:

1) If the battery is dead, it wont boot, even with the magsafe plugged in.

2) When a battery with power is plugged in and it has booted, when the magsafe is plugged in, the battery status says "battery is not charging".

3) Even if i take out the battery and just use magsafe, it doesnt boot.

4) The only way to boot is to charge a battery by plugging in into a working macbook, and then palcing it in the non-working one.

5) I have tried 3 batteries, so it is not the battery. (also, magsafe not working rules out the battery).

6) I already replaced the magsafe port, and it has the exact same issue.

7) I ran the Apple Diagnostic test, and returned "no issues found".

8) Magsafe lights up when plugged in. Can also reset smc, and the cable works on other laptops, so its not the magsafe charger.

9) When I say "doesnt boot", what actually happens is the fan goes on, adn the hard drive activity indicator goes on, but there is no display activity, and the fan stops spinning and the HD activity light stops being on, then it goes back on for a few seconds, then off, in a loop.

10) this loop starts even if i dont press "power", as soon as I plug in the magsafe (fan, HD light go on for few seconds then off etc).

What can this possibly be?