Macbook pro (2011) failing to start I have a 'slight' issue with my macbook and was wondering if anyone could help me please. 

Model: A1278 (EMC 2419*)
MacBook Pro "Core i5" 2.3 13" Early 2011
OS: Yosemite

The machine one day abruptly switched off while in use. The power button is ineffective and gives no response. To power the machine up, I removed the battery and attached the power cable.  

With the cable attached, the machine turns on. I have password protected the hdd, so the first thing it reaches is a pre-boot user selection. It allows me to use the trackpad and keyboard to enter this information.

From here, the machine begins to boot. It displays the apple logo and progress bar but abruptly shuts off around half way through the boot sequence. Once it has shut off, the power button is once again ineffective. To restart I have to remove and reattach the power cable. 

Resets: 
I have tried resetting the smc, pram, nvram to no avail. 

I have run an extended diagnostic hardware test which found no problems

Recovery: 
I do not have a recovery partition. 
I have tried internet recovery. I can enter the wifi details and it downloads the software I assume. Once it begins to boot, it shuts off before it gets to the recovery menu. 

I have also tried recovering from a USB, the machine shuts off before the menu. 

HDD: 
I have removed the hard drive and have attached it to my iMac via USB > SATA, I have found no issues there and can access the data.

Does anybody have any suggestions? 

Thanks in advance.
The problem was the keyboard. 

I detached all of the internal cables. The keyboard, the trackpad, the keyboard backlights, the optical drive, bluetooth and hard drive. 

I attached the HDD and a Keyboard via usb and started the machine by attaching the power cable. From there, success, it booted to desktop. 

I then started to reattach all until I found the culprit. Macbook now working minus the internal keyboard.