iMac screensaver hangs.

I have not been able to find a solution for this problem even after checking on Apple support and other places. The problem is irritating and simple to describe in that when the screensaver is running, sometimes when I go back to use the iMac (24inch, six months old) the screensaver will just freeze and take 1 to 2 minutes to let the desktop screen come back to life and the screensaver to disappear.

Not sure what else I can do for this.