This issue is almost always caused by a pop-up blocker on your browser.
Look for a "pop-up blocked"message on your browser main screen, which you can click on to allow pop-ups from timesheetz.net.
You can also navigate to your internet options/settings, and make timesheetz.net a trusted site.
WHAT YOU SHOULD BE SEEING
When connecting to Xero your main etz screen will have an overlay saying "Awaiting Authentication" and an animated loading bar.
You SHOULD also always get a pop-up window which commences with the text in blue "You are required to log into Xero before continuing, please click here". Like the below:
If you do not get this extra screen, it has probably been blocked by your pop-up blocker.