Why it does not turn on the console anymore?

Hello, let me explain what is going on, okay so i am good fixing video game consoles, i fix everything, so last time i got a Playstation 3 slim that i buy it on ebay, so i test it out and it works perfectly as normal. So i begin to make a tear down because i was going to clean the console from inside and i use the ifixit site to see the process of tear down. And i put everything back with the connections correctly and the screws, when i turn on the console work normally but after the working then it turns off, so i turn on the console again then in 5 seconds it turns off as weird. I search on internet and i check that what is going on and is as know as the "yellow light of dead" and the easy fix is to replace termal paste so that is because that happens after the cleaning. So i order the termal paste and termal paste remover in internet. After when i receive the products i begin the tear down, after i got to the motherboard i remove the old termal paste and i put the new termal paste, i put everything back so i looks okay but when i turn on the console but now it turn off quickly, so i continue to try to turn on but it does not work. So what i did is tear down again to check if everything is wrong and if the termal paste is okay, so all the console is okay so i build it again correctly and very carefully, after the building i try to test it out but it does the same, so is not the yellow light of dead because there is no yellow light after turn it on the console. For more details i made a video recording the happening.

So please tell me what is going on,what is the problem, what i going to do with my console, there is solution, or there are parts to replace, but please help me i am very worry and i love the console, if your are expert. but don't worry just explain what is going on tell me what is your answer.