my computer kept dying out after being on for a short time. took it to a shop and they said it would not be worth fixing. I opened it up and saw that the heatsink was full of ****, so I cleaned it along with the cpu, added compound, put it back together, computer comes on, will not load. ordered a used cpu, switched the cpu, and now there is no display at all. what could the problem be & how do I fix it?