If the gadgets disappeared from the sidebar, press the + icon and click the gadgets you want to use:
If they are still disappearing, remove the program from your computer (Control Panel > Uninstall a program) and install it again. Unfortunately, the software doesn't allow you to change the degrees to Celsius, but you can change the location. Right-click the gadget and select Set Weather location. In the provided window type your ZIP code or your current location (City,Country) and click OK:
