Have a look at some of these posts regarding 4GB players:
My Fake 4GB MP3 Player - Detailed Findings! from
here.
Fake MP4 4GB player - Files corrupted from
here.
4GB MP3/MP4 Players from
here.
I had 4gb now only 2gb from
here.
sc85052a FRUAD 4g from
here.
Maybe you're the first to get a proper on?
Do let us know how you get on with it.