Activities in P 3.0

Thanks colleagues for your help in past. I could not say thanks individualy but I got great help from you and i acknowledge that.

My recent issue is updating activities which start and then stop without finishing, then they start at another point of time and stop again without finishing and now i am expecting them to be started again in next week.
Please let me know how to break down them into different intervals of time, or any other way of handling them.

Please give answer in detail or in steps.

Thanks