Sony Xperia SP not turning On

Hi there, my xperia doesn't boot at all, red led (constant glow),

I tried back “ off” button (vibrates three times and nothing) + connecting to pc( nothing happens, pc doesn't recognise anything ) + manually charging battery to 3.7 volt and connecting to phone (and again nothing)

Now I stripped it down and wondering why is this happening.

P.s when I connect charger the voltage at battery connection dock is 1.7v*******which I assume is a side effect of dead power management IC ,am I right?