Windows 10: Can't install programs from "Unknown"?

I've been trying to install a program that I know for certain is safe - however I am getting completely blocked out of it by Windows, and it's telling me to "contact an administrator". I am an admin on the account, I checked. I also even went as far as to make a new account that's an administrator to try and run the program. It's my own damn personal computer. I have never had this issue in the past, all that would happen was a warning and the option to run anyway popped up. Now, I even get a little watermark at the bottom of installers saying "this file does not have a valid digital signature". I'm not a toddler. I know how to use a computer and how to tell whether a file is safe or not. I'm even running Windows 10 Pro, which, one would assume it wouldn't coddle you in this fashion. I've even gone as far as to disable features of Windows Defender, and it still completely blocks my file from running. What the hell is going on?

:)

 

unlock sim t-mobile lumia 521

Thanks for your suggestion, but this is a prepaid phone --- no contract. As I said T-Mobile lists the number under an unknown carrier and suggested I contact Microsoft.

 

Why did the startup window get cleared?

I didn't missed any step, the list was gone and gone , even after using lot of programs the programs were not listed in that list.

 

windows xp installation and dual core am

could someone please list the steps they follow to install windows with a dual core processor and windows xp service pack to. I'm reletively new to amd dual core and i feel i'm missing a step. All help will be appreciated. thanx