Something seems to have changed.
The tablet now starts up on a widget page.
How do I set the "start up" page I want it to display?
If you just tapped the power button to put into sleep mode and then tapped the power button to wake it up again... after going past the lock screen it will (normally) return to whatever screen you last left it on. To exit that screen either press the return/back icon at the lower bottom left, or press the home icon just one over to the right.
Otherwise, if you have not installed some other user interface (or 'rooted' type firmware)... you could just totally turn off the device by pressing and holding the power button for about 15 seconds. When you next power up the device (and after passing the lock screen) it should (by default) always come up with the central home screen.
Other than that I'd have no idea what problem you are having. The Archos G9 tablets basically work like any other Android device (except for some flaws in certain firmware versions anyway).