Thanks for reply Wojciech.
I have not changed anything in solid works.
Everything is as it was.
Due to a camera issue in my machine the Dell tech support gave a link to their latest chipset driver update.
May be that update causing the issue!
I've seen a lot of people complain (rightfully so) that Windows 10 auto updates replaces the video driver. This could render the Quadro benefits like anti aliasing null and void.