
4 answers
What do you mean by 'data loader (or sales force) changes the value of date'?
Are you saying that you are uploading data with a set of dates and the dates are then different when you check them? Or are you saying that you are having trouble uploading date fields because you have the wrong format?
If it is a format issue, take a look at this helo dic, it gives you what formats Salesfroce can accept when uploading Date and DateTime Fields with data loader.
https://help.salesforce.com/apex/HTViewSolution?id=000004680&language=en_US (https://help.salesforce.com/apex/HTViewSolution?id=000004680&language=en_US)