The most common I run into is dust, lint buildup. You can usually find out if the owner is keeping up with maintenance by asking about their canned air use.
Also, boot safe mode with networking while you tell more about your PC's care, make, model, age.
Today i was working on my laptop then suddenly a blue screen appears and my computer started shutting down and then restarted. After that i myself shut it down and then restarted again. Windows then logged in and after one or two minutes again blue screen appeared and my computer restarted. It keeps on shut down and restarting. I dont know what is wrong. I have not experience this before. Plz help me. What should i do? I cant check my computer settings even. Because when i starts windows, the blue screen appears after one minute of logged in.