[tay187]

Ok... I bought a Macbook Pro on eBay (knowing before hand it would need some work).. Now that that's out of the way.. here is what's happening: I will try to list everything that is working or known to be not working:

* The power cord is green unplugged and orange when plugged in
* I press the power button and it turns on (no chimes) and the fans kick on to full throttle for about a min and it shuts off
* Nothing shows up on the screen
* I have a bootable USB drive in it, it lights up when the power button is pressed, but then turns off after about 5 secs
* I opened it up and pulled the logic board with no signs of anything spilled on it (not meaning there wasn't) but nothing noticeable
* The far right side temp sensor looks to be slightly broken? But still plugs into the board
* The RAM is good (pulled from a working laptop)
* Plugged in a DVI monitor and nothing shows up on it either
* Nothing looks broken on this inside as far as the logic board is concerned
* 2 wires (the blue and the grey) are broke off the part where the battery sends power to the logic board - I know I need to get this either replaced or re-soldered
* The PRAM battery is missing

Wow... A lot was said... if anyone has any ideas about where to look or what to do next... I'm all ears!! Thanks

[macaddict0001]

Some machines will not boot without a pram battery, not sure if this is one of them, and they named the pram battery something else with the intel switch, not sure what that was either.
If the temp sensor is broken the circuit is probably open. The computer would either interpret that as max temp reading or min temp reading depending on if the sensor has a positive or negative temperature coefficient. That could cause the computer to shut down after booting as well as the full fan problem.

[AKcrab]

It's now called the "backup battery".

No internal or external video is probably going to be a new logic board.

[Waragainstsleep]

Leaving temp sensors off on an MBP will not cause it to shut off, that feature is built into the CPU and its core temp. The detached battery wires don't sound good, but again should not cause any issue unless they are shorting each other maybe. I would disconnect that connector. The MBP does not require it to run. I do find it odd that the battery seems to be charging (have you checked this) despite this damage.
The backup battery is the most likely reason suggested so far. It might be worth buying one if you can find one reasonably cheap, but be prepared to say goodbye to that cash in case you can't get it running.

The fans being on full blast could indicate a temp sensor issue, but like I say it should stay on for a while and even boot fine if it has a good OS to boot from.
Firmware issues can also cause the fans to run full. If the unit is not booting up or even trying (Which sounds like yours), this also points to a potential firmware problem. Two things to try here. Firstly use another Mac to download and burn the appropriate firmware restore disc from Apple. Put the disc in the Pro and hold the power button down to power on, but keep holding it. You should get the LED to flash eventually (takes 5 or 10 seconds holding the power button). This means the Pro is now trying to restore its firmware from the disc. If its going to work, this should sort the problem for you. Make sure you use the correct disc. There are upwards of 7 different versions last time I looked I think.
If the restore disc does not fix the issue, you should try the technicians most most drastic technique: The minimum system. This is a general principle when conducting hardware diagnostics, so may interest anyone with a tricky issue. You need to strip the machine down to its most basic components. Only the things that are absolutely necessary to run. For a MacBook Pro, you need the logic board, RAM, left I/O board (and the cable to connect it to the logic board).
Believe it or not, that is enough to run. To be properly thorough, you should try this without the case. Correct procedure would be to connect the left I/O to the logic board with a single stick of known good RAM together on an ESD safe mat. YOU WILL NEED TO HAVE THE HEATSINK ATTACHED TO THE BOARD WHEN YOU POWER IT ON. Failure to do that will cause the CPU and/or the GPU to die. Possibly in quite spectacular fashion. (Some old G4s literally EXPLODEd, and these Intel chips are hotter as a rule). Connect your naked MacBook Pro to an external monitor via DVI or Displayport. In order to power on without the top case attached, you need to find a pair of solder pads on top of the board marked "PWR". Shorting these when power is connected should power it on. You might wish to leave one fan connected, just so you know its on. You should get a flashing folder icon with question mark on the external display.
If it works out of the case, you can reinstall it and try it again. If it still works, you just reconnect everything else one part at a time, testing in between.
I have seen faulty screens prevent booting before but a faulty optical drive is probably the most common to cause these exact symptoms (You might want to try disconnecting that one and testing before removing everything from the case). Otherwise it could be anything including a cable or connector.

If you get no external video from your minimal naked system, I'm afraid your logic board is probably faulty. (Again it could be the left I/O board or the interconnecting cable. These parts are much cheaper but if you want to take a punt on one or both, make sure you get the right one. They all look similar in Alu MBPs but are not interchangeable with different generations of logic board).

You should brace yourself for a logic board fault to be frank. There are a lot of faulty Mac notebooks on eBay which claim to have different kinds of minor damage or just 'mysteriously stopped working one day'. Sadly many of these have been thoroughly tested by previous owners who eventually learn the board is fried and its not worth buying a new one. Given that yours has detached internal battery cables (Never seen this, even in damaged ones), its likely someone has already messed with yours. Doesn't sound like he was much of an expert either, so he could easily have zapped one of the chips with static while he fumbled around inside if he wasn't taking the proper precautions.

Hope that helps you out. Maybe you'll get lucky.