Laptop crashes randomly.

I own lenovo z480 for 3 years. My laptop was completely fine and was in great condition until when its charging port became loose. I fixed it by disassembling the laptop. Then the laptop stopped charging. I had to plug the laptop to work and because of random abrupt power cuts in my area, the laptop had to go through many abrupt shutdown. Finally, I took it to service center and they fixed it. However, my laptop began to crash randomly. It just began to be unresponsive randomly. I took it to the service center again. They told me that my graphic card in the motherboard has been damaged and the motherboard need to be replaced. I had no choice so I said ok, then they replaced the motherboard with manufacture refurbished motherboard. However, the problem still persist. Again, I went to them. They said my hard disk had crashed so it need to be replaced. Again, I had no choice. I replaced that also. But, still the problem persist. Now, they said that my processor is damaged and need to be replaced. If i replace that then it would mean I replaced all the main components of laptop except the cover. Also, It costs a lot and I don't know if that will fix the problem or not. I want to know if bad processor can cause such problem or not? Please, suggest me.
Detail of Crash before I took my laptop to service center:
Most of my work require internet and the crash usually happened while browsing. The crash was random. Sometime, it crashed within minute of starting, sometime, it crashed in hours. A pattern i have noticed in the crash is: the more I use the laptop, the rate of crashing increases and the laptop crashes quicker and quicker. And, the laptop began to crash while loading windows and then at the boot screen. Finally, the laptop switches on but no display is seen. At such stage, If the laptop is allowed to rest for few days then the laptop becomes usable and the above process repeat.