[hgir]

On your tablet, select Settings>Applications>Manage applications, scroll to find MS and tap on it.
A screen will pop up. Select "Force stop" to stop MS if it's running, ignore the warning about it maybe causing a problem.
Then select "Clear data", which should also clear the cache.

When you relaunch MS, it should be as if it's a new installation, therefore, it may require you to go online to authenticate the license, assuming you're using the full version.

Thanks for the instructions which I will file away. As a new user I made a simple mistake - instead of pressing "Songs" I had selected "Recent". So all my songs were there after all.