MS Project 2000

MS Project 2000 (on calendar) shows year March 2004 … but when it goes to April it becomes 2005. The dates in the project as listed right but when you want to look within the month range it skips a year. I have reinstalled the sw. If I open blank project, year is right. When I open existing projects, year goes wrong and will not go back. WHAT IS WRONG — WHAT TO DO?