MP 5,1 Stalls at logo, won't boot

[Guest johnvision]

mid 2012 MP 5,1 suddenly will not pass the apple logo loading screen. The loading bar stalls at around 75% but reaches 100% eventually, however stops there and never proceeds further.

 

Apple store have assessed and can not figure it out. I have since installed another backpane and the same issue occurs

 

Source: MacRumors