Dimension Freeze During Render

Ill try to be as thorough about this as possible.

Dimension is freezing and slowing down my entire machine during Render. 

This isnt happening when I create a new scene, place an object, color it, place a graphic on it and render it.

This is happening when I render an object then go back and change out lets say the graphic on the object and then go to render that so it is at the same angle, lighting etc. When I go to render it for a second time it completely freezes and the only way for it to render properly without freezing is to start all over. 

Any ideas why? Make sense?