power on, no window boot up

Yep well I agree with what Mellon Head has said re hardware and I still think a look at the state of the CPU cooling would be worth it given that the problem is intermittent. It will not cost you anything to do after all eh?

But if you do end up with a non usable machine the data can always be retrieved from the drive using another machine

Thermal compound is a paste that allows heat transfer between your computer's CPU and it's heat sink. All current computers have to dissipate heat somehow, and most do it by having some sort of metal block with radiator fins on it attached to the CPU to radiate the heat away from the CPU and to keep it cool.

Unfortunately, the metal casing of the CPU and the metal block of the heat sink do not make for a good thermal connection because of very small voids in the metal in the two items. Thermal compound is therefore spread between the heat sink and the CPU, to fill the voids, and that allows the heat to transfer more efficiently. Think of it like a peanut butter sandwich. The two pieces of bread are the CPU and heat sink, and the peanut butter is the thermal compound between them. The peanut butter holds the sandwich together, much like the thermal compound allows the heat to transfer to the heat sink.

Now, the big problem to investigating your thermal compound is that you would have to disassemble your laptop to see it, which I don't recommend that you do. You can, however, check your temperatures, if you can get Windows running again. If you can, you can download HWMonitor from here:

HWMONITOR | Softwares | CPUID

and install it and run it. It will tell you the temperatures of the CPU and graphics card. If you can get it running and can do this, please take a screenshot and post it here in this thread so we can look. Here's how to post a screenshot:

Screenshots and Files - Upload and Post in Seven Forums

You can take a screenshot by using Window's Snipping Tool, found under Accessories in the start menu.

Ok mate just to give you a rough idea of what you will be looking for see my pics and as I say boards differ from maker to maker but the principles are the same.
Plus I use these for all renewals of the compound but the choice is yours of course as there are others around I just happen to like the cleaning method and the compound.
Arctic Silver Incorporated - ArctiClean

Arctic Silver Incorporated - Arctic Silver 5

PS Meant to add that this is how you can change the CPU if necessary the GPU if separate is usually soldered into the board