My late 2013 iMac is slowly driving me mad with how slow it's become over the years. I'm running Sierra 10.12.6. It lags on any app – literally took over 30 seconds to loads the content in the side bar in Mail just now (the content of the message below the title). New tabs in Chrome take 2-3 seconds for the favourites to display. When I shut down, it takes a while to switch between applications… it's generally as if it's processing more than it can cope with – I guess a good way of describing it would be if you were in a Mac shop testing it out you'd walk out the door thinking my phone's faster than that!
It's very slow starting up – it's hit or miss as to whether image files on the DT display as the default non image icon or actually load the preview of the file. And on the subject of preview, somethings it thinks about showing those for a few seconds too! I just know it should be much faster, instant in fact, but it's like it's clogged and needs more power.
I feel I want to do a complete erase and reinstall but will that actually do anything for the effort involved? Could it be a virus? One thing I am certain of is Chrome has something weird going on where it opens a new tab on certain pages – annoying when you're filling out a form or typing like I am now (not a proficient typer so 90% of the time I am looking at the keyboard) and when you look up, it's opened a new tab and nothing's been typed! Aghhh! Are these things connected??
Grateful for any help.
[Re-Titled by Moderator]