Laptop won't start after cleaning and applying new thermal paste

Hi, Recently I decided to clean out my Toshiba Satellite Pro laptop, given that it just so dusty it was constantly overheating. I spent an ardious 3 hours to remove all of the factory sealed screws by hand, then I dusted out the CPU fan with an air spray can, and finally applied new thermal paste. After assembling it back together, I come to find that it will no longer turn on! When I try to charge it, the lights on the front pulse for a second, then cut off, then pulse etc. If I had to guess I would say this is a CPU or PSU problem, and perhaps I failed to assemble the CPU back together properly? I was also grounded the whole time. I'm almost certain everything is back in place, including the wires. Any help would be appreciated. EDIT: There is also a clicking noise coming from the PSU.

Did you try to run it without the battery or only on battery? Is the clicking noise coming from the external PSU?

With the battery. Oh, and when I said the clicking noise was coming from the PSU, I was mistaken, it was actually comming from the DVD drive, which is one of the first components to start up on my laptop. I've taken it apart again and to tell you the truth I can't see what I've done wrong. There's a chance some static reached the CPU, thereby damaging it, but I still doubt it. At worst, I may have accidentally detached the heatsink from the CPU, but I fitted it back on perfectly just after.

Anyone?

Did you remove the CPU or only the heat sink?
Take out the PSU and the battery and check your memory. Clean the contacts with a contact cleaner. Be sure to place it well into the slot.

and finally applied new thermal paste

Why? Note that TIM (thermal interface material) will easily last 10, 15 years or even longer AS LONG AS the cured bond between the mating surfaces is NEVER broken.

You NEVER need to replace TIM just because it is X number of years old. Remember, the purpose of TIM is to ONLY fill the microscopic pits and valleys in the CPU and heatsink mating surfaces to push out any trapped insulating air. Even if the TIM has dried out, it does not need to be replaced because the solids that remain are still occupying that space preventing any insulating air from getting in.

It is the solids in the TIM that do the work. The ONLY reason TIM has any liquid component to it is so it can be squeezed out of the tube and spread across the device easily, evenly, and smoothly.

If anyone says TIM needs to be replaced just because some arbitrary amount of time has passed, demand they provide a link to any CPU or GPU maker, motherboard maker, PC or notebook maker, graphics card maker, TIM maker, white paper or technical study that says TIM needs to be regularly replaced.

There are two main problems with replacing the TIM. (1) Too often the CPU or socket is damaged due to mishandling - typically due to ESD or rough handling. Did you take the essential ESD control procedures? Note a static discharge (spark or electrical "arc") from your finger tips can torch a Grand Canyon sized trench (microscopically speaking) through 1000s of transistor gates on a CPU - yet the ESD can be so tiny, you (we as humans) are incapable of feeling, seeing, or hearing that discharge.

(2) Properly cleaning the mating surfaces is also essential. You never - as in NEVER EVER - just add more TIM. You MUST always thoroughly clean the two mating surfaces before applying a new layer of TIM. And then the new layer of TIM MUST be properly applied. It must be a thin a layer as possible while still providing complete coverage across the CPU die. The most effective transfer of heat occurs with direct metal-to-metal contacts of the mating surfaces. So any excess TIM is actually in the way and counterproductive to the most efficient transfer of heat.

Cleaning the interior of our computers of heat trapping dust is essential (and unfortunately, a real challenge with notebooks). But replacing the TIM just because it has not been done before or in awhile is not.

You say you were grounded the whole time - grounded to what? You don't need to be grounded to "Earth ground" but you do need to be grounded to the computer - that is, you and the computer must be at a "common ground". This ensures there is no "difference of potential" between you, thus preventing any "arc".

Then you said there is a chance static hit the CPU. That is my fear too.

Okay, I've managed to get it working again (onto the login screen) with only minimal physical damage in the form of a busted touchpad, although it doesn't really matter given that I only use the mouse anyway. Right now I'm trying to get the keyboard back on, which is providing to be really irritating and fiddly. Once I've done that I should be able to log on and check the temperature, and all of this should hopefully be worthwhile. And don't worry I made sure to clean off the old, residual paste before applying new paste.

If the touchpad and / or the keyboard isn't working is because the flat cable wasn't fit correctly into the slot. That's why I don't like laptops.
Just to know, what was the problem?

https://i.imgur.com/vlFfCZ5.jpg

Okay all is good now. It took forever, but I've managed to reassemble it successfully, and now the temperature has decreased. Under high-load it used to overheat, but now it maxes out at 75c.

It was all worth it in the end. Thanks for the help.