Time keeps changing

[Sambo110]

My iMac's time keeps changing everytime it shuts down. Sometime only an hour ahead, but then it was like 21 hours ahead, 1 o'clock Monday. Any reason why?

 

[iLog.Genius]

My iMac's time keeps changing everytime it shuts down. Sometime only an hour ahead, but then it was like 21 hours ahead, 1 o'clock Monday. Any reason why?

Reset PRAM:

On boot, hold down command+option+P+R until you hear 3 startup chimes, after the third one, you can release the keys. Once in OS X, set the correct date and time and restart and see if the changes saved.