That is a question with no details which would help us to help you. There are numerous reasons why a program, including version 9, would stop working.
1. What computer operating system.
2. How has the program stopped working? What error messages if any?
a. You cannot open from the desktop icon
b. You cannot get into the Timeline or Sceneline workspaces
c. You get into the workspaces but the program crashes on you
d. Are you working with an Internet connection?
2. When was the last time that the program worked for you so that you completed a project successfully.
3. Are you working from the 9.0.1 Update?
4. Is your video card/graphics card driver version up to date according to the web site of the manufacturer of the card?
5. Are you working with a pen and tablet device instead of mouse?
6. Is your computer optimized, updated?
Let us start here and then decide on troubleshooting strategy.
Any questions or need clarification, please do not hesitate to ask.