How to carryout Re-scheduling

hi,

A project is being created with service activities and internal activities. There are about 40 internal activities. Now as the project is scheduled and as it progress activities are confirmed ( about 20 activities). Now due to some reason the project is on hold for 4 months. After 4 months the same project is being started , now the remaining activity date has to scheduled according with out changing the dates of the confirmed activity. How to do this ?