Website Privacy Error problem

I know that Type Drawers is not really the place for this sort of thing. I have had my website www.g-type.com since 2012. Since last October I have had a completely new site with the same address. The problem I have is that I haven't been able to view my own site, old or new, for at least 5 years on my own computer. I can view it on a phone, iPad, Macbook etc. but not on my main iMac. As you can imagine this is very frustrating as I thought it would be solved with the new site. I have tried every fix I read about on the internet, and even had 'experts' come to my house to try to sort it. Still no joy. Any ideas anyone? This is the image that always appears. Yours not very hopefully, Nick.