I've already emailed reFX support but while I wait I figured I'd ask here...
 
I always used reFX Nexus 2 with Sonar Platinum in the past. But this week I just reformatted my computer and upgraded to Windows 10 (from 7) and am in the process of reinstalling everything.
 
Nexus2 installed fine from what I can tell, but when I load it up in Sonar, the VST window appears blank (just straight white). If I hit keys on my keyboard, it plays the initial patch that's loaded when you load Nexus2, so it's working, it's just like not drawing the GUI. All my other VSTs that I've tried so far load fine.

This is the 64 bit version of Nexus2, Sonar Platinum, and Windows.
 
Any ideas?

Did it install a standalone version?  If so, try that and see if it acts the same.

No unfortunately not. Also after posting this i tried installing the 32bit version and it works just fine.. so it's only the 64bit that's having the problem but I'd really like to stick with 64bit if I can

Could be a graphics (card) issue...
 
Make sure you have the latest drivers for your card.  Especially important if it's an older card (or if you let Win 10 load it's own drivers and it's causing problems).

yeah that's a good point. gonna check now. it says my graphics card drivers (AMD Radeon 7700 series) are up to date but thats through windows. i'll download the official drivers and see what happens...

well leave it to me to do 2 things at once so i'm not sure which fixed it haha, but i updated the graphics driver (even though it showed the same version number as the one windows supplied) AND reinstalled nexus2 as administrator... but one of the two fixed it haha. i'm gonna give you the credit JonD, even though it might have been me ;-)

Lol, glad to hear I might have helped.