@all of you who helped me with really usefull advice when I had problems with both my Outlook 2010 and my intrusive pop-up: I finally ran Malawarebytes twice: once on a normal session and that got rid of some problems, and Outlook started working normally again (together with thousands of emails flowing back into my accounts lol) and then I ran it in safe mode, and that got rid of the pop up! You guys saved me both money (no need to buy a new PC) and time (no need to get this one fixed)!

so thank you all in the forum for your very kind and great feedback and invaluable help!