Question Laptop does't turn on after changing thermal paste

[Fer Carnu]

I have pretty old (5 years) Asus x542ba which I decided to clean its fan and change the thermal paste.

I have removed the keyboard, the battery, the hard disk, the DVD unit, the fan, the main board and lastly the heating on he cpu, under the main board.
I cleaned the old paste from the CPU and the heatsink and I noticed the CPU was integrated inside the board (didn't have a socket) and had a translucent orange "sticker" between the outside of the CPU and the heatsink. I removed it because there was some thermal paste under it.
I put it all back together and it doesn't turn on anymore, but in a really weird way: when it's not plugged in, just with the battery, there is no power led, no nothing, it's completely dead; when I plug it in it wants to turn on, the power led is on, the the battery led is on (as it is charging) and the hard drive led blinks twice. After that second blink I can suddenly hear the HDD turn of, just like when I force a power off and the other leds turn off as well. Even more interesting is the fact that in both cases the fan doesn't start spinning at all.
The paste I used is Thermal Grizzly Hydronaut, which is not conductive.
I disassembled it again quiet a few times to check I didn't forget anything, I reseated the RAM, I put back the "sticker" on the CPU, I checked all the ribbons and I ried with and without the battery connected.

 

[Ralston18]

This:

"and I noticed the ? __ was integrated inside the board (didn't have a socket) and had a translucent orange "sticker" between the outside of the _CPU CPU the heatsink. I removed it because there was some thermal paste under it. "

What is the ?

Also some typo regarding "CPU CPU" as I underlined.

What, if any, problems were occurring that led you to decide to clean the fan and change thermal paste?

My thought is that perhaps one of the cables or connectors was damaged during the initial disassembly and re-assembly.

Another thought is that there is some problem with the thermal paste and/or how it was applied? What instructions did you follow? Source?

All I can think of for the moment is to try a very careful re-application of the thermal paste. Hope being that a thermal shutdown is taking place and that nothing is physically broken.

 

[Fer Carnu]

This:

"and I noticed the ? __ was integrated inside the board (didn't have a socket) and had a translucent orange "sticker" between the outside of the _CPU CPU the heatsink. I removed it because there was some thermal paste under it. "

What is the ?

Also some typo regarding "CPU CPU" as I underlined.

What, if any, problems were occurring that led you to decide to clean the fan and change thermal paste?

My thought is that perhaps one of the cables or connectors was damaged during the initial disassembly and re-assembly.

Another thought is that there is some problem with the thermal paste and/or how it was applied? What instructions did you follow? Source?

All I can think of for the moment is to try a very careful re-application of the thermal paste. Hope being that a thermal shutdown is taking place and that nothing is physically broken.

I fixed the typos.

Well, it used to overheat, one time I even shut down because of that and the fan was always really loud even on idle. When I opened it the fan was very clogged with dust.
I would think that at least the fan would start spinning for a split-second before it shuts down, but I will try reapplying it.