Been working on a laptop recently for boot up problem at start up...tried taking out the cmos battery and so forth but still the same..till I figured that due to a small shiift of the harddrive from it´s position which may be caused due to a hard hit or something causes short in contact. so i just took it out and placed it back ensuring that it is directly in the slot and tight..so shorting of harddrives can cause boot up failure sometimes in laptops
I remember I had a problem like this, as soon as I powered on my laptop it would shut off after 1-2 seconds.It was a motherboard issue. I remembered it started happening when I shut down my computer by holding down the power button. After that, I've never shut down a computer like that.