Project Start Date

I have inported tasks from an excel spreadsheet to microsoft project. This has set the project start date. I have tasks that are before the date I began to build up the programme. I have added all links to the programme. When I am trying to reset the start date to the actual beginning of the first task it drags all the items linked with it. Can anyone tell how to change the start date but leave all other areas unchanged, e.g. durations, links etc.

In other words I just want to remove the enbedded start date which is when I first started to produce the programme?