what sort of graphics card do you have?
does the game eventually un-freeze?
does nightfall occur?
That used to happen to me too, until I upgraded my graphics card.
It'd only last a minute or two until my old graphics card could render the lighting from day into night and vice versa.
For your contests- if you don't need night time shots, you could use the set hour cheat. Open your cheat box, type in sethour 8
(think military time when choosing and entering a number)
voila, it's 8am.
Also, there's a hacked object on MTS2 that will make it daylight all the time on the lot that it's used on. Fair warning though, I've used this for a contest once and was not able to switch it back to normal.
http://www.modthesims2.com/creator/showthread.php?t=239029