Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
Sorry you originally posted this question in Computer category instead of Mac category. The other expert is a PC Expert.
First of all I must warn you. The sudden slowdown and spinning indicates usually happens if there is any issue with the hard drive, either it is failing or the system file are corrupted. So I want you to get an external hard drive and backup all your important files ASAP. It is not safe to do any troubleshooting without having a backup. Once you did that, post a reply in here and we can start troubleshooting