Hi,
since it stopped working for no apparent reason, my guess is that maybe there's something wrong with your Java JRE. Please open a command line (that's Windows-key + R, type "cmd" and hit Enter) and run Arduino from in there. It sould work by just typing "arduino.exe" and hitting enter. If there is an error with Java (i.e. something like "java.lang.NullPointerException"), post the output in the CMD window here.
gz John