That is a really heavy usage from a notebook, I think the type of notebook selection is important, like Dell have Latitude series which would be for such heavy usage vs their lower end casual usage, likewise Lenovo T series would fit into your usage requirements.
The problem could be that your current notebook was not designed for heavy usage, just my 2 cents.
if its overheat the motherboard will have auto shutdown.it will be able to reboot after.
HDD blinking light?
smth like tt happen to my desktop too. it was the videocard bios not being able to load. bcoz u cnot clear the videocrad bios u cnot go into system bios...
nope,i still get a black screen whenever i hit the power on.
is it cover under warranty?
I doubt it's heavy usuage cuz i use it 8 hrs straight in school,air coned enviroment and start using it around 8pm in the nite for 4 hrs.