VST's invisible in cubase 7

Hi, I’ve just installed a copy of CB7, all works very nicely.
I also installed a couple of synths Sample Tank and another cheepo - The’re not showing up in Cubase
When I was installing Sample Tank I got the message
’Default VST path not found in registry’
(I’m still learning about computer DAWs and I don’t know what this means, or how to correct it.
The dll’s are showing in the VST folder - they don’t seem to be blacklisted. I don’t know where to go from here.
Can anyone help please,
with thanks