I used to do at-home computer troubleshooting as a part time job when was in college. Most of time it was just opening up the casing, dusting it and reattaching

I used to do at-home computer troubleshooting as a part time job when was in college. Most of time it was just opening up the casing, dusting it and reattaching all the parts/reinstalling Windows that did the trick. 90% of time it was just RAM popping out a bit. But in rare cases, it was the components themselves. I used to rely of these shops in the city (Hyderabad, India) that fixed motherboards etc. really cheap and relatively quickly (less than a week most of the time). People that worked there weren't engineers or anything, more like tradesmen. It was amazing to see them work.