The Panel clock applet in Ubuntu 14.10 suddenly stopped showing the correct time and date! I tried restarting, but it does not work.
Select System Settings -> Time & Date -> on the line at the bottom of the Time & Date window that says: Set the time: select Automatically from the Internet.
If that doesn't work, enter the BIOS when the computer is starting up and change the System Time and the System Date in the BIOS settings to their correct values. If the System Time and the System Date in the BIOS are repeatedly losing their correct values, this could be caused by a worn out CMOS battery.
If that doesn't work, you may need to replace the CMOS battery on the motherboard. The CMOS battery usually looks like a thin silver disk the size of a large coin. The model number is usually engraved on the top side of the CMOS battery.