OK - can only recommend the drastic "Factory Reset" - and you may well judge this is not worth the risk and effort.
1. Back up EVERYTHING on tablet - photos, mail, settings, passwords.....
2. Perform factory reset - this sets the tablet back to "new" condition
3. Restore everyting and install and setup Skype and other software.
... not for the faint-hearted. It did work for me to fix an Android phone issue - but it took me a while to get everything back on the phone that I use.... your call.
