MBP cannot reach boot screen after trackpad replacement

A work colleague came across an issue with her MBP 15” Late 2011 where the trackpad completely gave up working and the keyboard behaved very strangely, some key presses may have registered, if they did they took a while to appear on screen.

I offered to take a look but didn’t have much time. I saw I could get a replacement trackpad cheaply so I ordered it and replaced the trackpad with the battery disconnected. The laptop had been asleep rather than fully shut down prior to the battery disconnection, I forgot it wasn’t shut down properly. I did the replacement over a few weeks with the bottom case removed and everything stored in a dry cupboard in that time. I’m not aware of anything happening to the laptop while it was in the cupboard.

After reassembly, I went to power it up. The sleep light lit up bright then went dim, fans started, hard drive spun up, but nothing else. No caps lock, no chime, and nothing on the screen. The fans progressively build up to full speed. I’ve let it sit like this for around 30 mins a few times and nothing happens. If I press and hold the power button to shut it down, then press it again to restart, it enters a boot loop of fanning up, spinning the hard drive then cutting it straight back out with a click and starting the same again over and over.

I’ve tried getting it going with the battery being connected and disconnected, with trackpad disconnected, new trackpad, old trackpad, keyboard disconnected, hard drive disconnected, 1 ram in, 2 ram in, no ram in, all key combinations at boot. Nothing makes a difference. I can’t do a PRAM reset, the system can’t get far enough to chime once. SMC reset does cut the power but doesn’t fix anything. I don’t have an OSX install disk to try and boot from but I don’t think it would boot from it anyway.

I’ve had a good look at the logic board and can’t see anything glaringly obvious, nor am I aware of anything happening to it. I don’t believe the machine was water damaged, but the logic board certainly exhibits all the signs that it has a problem. Hard drive contents are still intact after checking on another machine.

Can anyone suggest any steps to try? See a photo of logic board attached, I presume it will be requested. Please let me know if better quality is needed.

Any help would be appreciated, thanks.

James