so i have this IMAC 27'' late 2015 model, due to relocation had it packed up and off for a few months, now after 3 months its not powering on, tried pressing the power button in all sorts of ways, took it to repair shop and they're telling to replace the logic board, cant say if theyre genuine or what, asking for 500$ to replace it, is it really that costly for an older version of mac. is it really the issue of logic board if a mac doesnt power on at all or are there any other way to fix it like changing some sort of power supply board or anything. please help