OK so it originally came with Leopard and I have progressively done all of the upgrades. At Lion, it began to give me the spinning beachball whenever I try to do practically anything. I then did a clean install of Yosemite (current) and it was fine until a few weeks ago. Same issue now. The beachball occurs when I open Mail, iTunes, Safari, Firefox, Chrome and most other applications.
In an effort to troubleshoot, I tried logging off of my profile and using the guest account.
Guess what? No beachball at all and the system is responsive.
Any suggestions as to what I could do to fix my profile or whatever? LOL
Screen shot of my machine.