Angels have the Phone Box
Hi trudic and welcome to Tenforums.
It would help to know if you could identify or at least describe what type of popup you were seeing.
Please fully fill in your system specs so we know exactly what we're dealing with.
When you first turn the computer on, do you see the manufacturer splash screen/logo, before Windows starts to load? Because if you don't, that would indicate a graphics failure of some sort.
If you can see the initial splash screen before Windows loads, then it's not a graphics problem, and you could try booting the system to Kyhi's custom rescue media, and run MBAM (Malwarebytes) from it.