This is complicated but I'll try my best to explain. My computer got messed up due to one of thos buggy windows updates. I had to go back and re-format the entire drive and then re-install from an old system disc image I made in 2014.
 
SONAR Home Studio 6 was already installed on that disc image. So was the VST folder etc. Everything worked ok. 
 
Then I installed SONAR X3. I did not un-install Home Studio 6. 
 
Some stuff works in SONAR X3, when opening an old file. A lot of the VSTs are missing, I'm assuming I have to reinstall them. 
The drums dont sound at all, even tho if I insert a soft-synth, the menu shows the package (EZ drummer, known in SONAR X3 as DFH sampler) is loaded.
 
Should I try to install all the VSTs and EZDrummer again, or am I asking for trouble?

There's no harm in re installing VST's, the worst that happens is you'll end up with 2 of the same VST in the folder. 
Did you also run the X3 e patch? that's important.