Steinberg Cubase 5 DAW does not have folder for VST 2.x plugins in standard location.
This results that Cubase can't find you favorite plugins that you install before Cubase 5 installation or plugins installers are being confused and not knowing where to deploy them selves.
Fortunately, this is easy to fix and we have several options here.
For band new plugins installation you may want just to install your VST 2.x instruments or FX plugins to VST2 folder that Steinberg cunnenly hidden in C:\Program Files\Common Files\Steinberg\VST2 .
Alternatively you may install your plugins to any existing VST Plug-ins folder that you might already have and just add this folder to Cubase 5 VST 2.x Plugin Paths, so Cubase would know were to find them.
The latter solution also will help Cubase to find any previously installed VST plugins that you are so struggling to get working.
So, all you need to do is the follwoing:
To ensure that Cubase updates it's settings click "Update" in "Plug-in Information" window.
You may want to repeat the procedure for all VST folders (if you have more then one on your computer).
Voila! now you can access your favourite instruments and effects plugins.