Windows 7 Ultimate Sometimes Chinese Characters Show Up As Squares?

have been having this problem for more than a year, my windows 7 ultimate is able to recognise and display chinese characters in the past, but very often, sometimes the chinese characters doesn't display properly, and after i restart the operating system, it shows up fine. is there any problem with my OS? majority of the time it shows the chinese characters properly, but often it messes up the chinese characters and displays squares.