Tablet won't install Non Google Apps.

I've purchased a China Generic Tablet with Jelly Bean O/S.
It came with many Apps pre-installed.
I have a Google a/c. and have downloaded and installed several Apps through the Google Store.
BUT, how do I install non-Google Apps?
The "Settings-Security-Unknown Sources" is ticked.
They download and Install, but, they're nowhere to be found.

Have I bought a Dud?
or is there some way to get around it?

Any suggestions will be helpful.

The Google Play store probably doesn't recognize the device. [Only registered and activated users can see links. Click Here To Register...]

You could use an alternate market app like Amazon.