I bought a used laptop from neighbor a few months ago. (husband passed away) It got so hot I could not have it on my lap without a towel or something similar under it. A few days ago, it started shutting down after about two hours. I let it cool and it started back up ok, but continued the shutting down. The last time it shut down it stayed down! I'm assuming it's the battery? I know nothing about laptops but this would seem probable. Advice?