-and more help in http://helpx.adobe.com/creative-suite/kb/invalid-serial-number-cs4.html
When you ask a question you need to provide some basic information
-Forum quick start https://forums.adobe.com/docs/DOC-5601
Mac or Windows, and EXACTLY which version of the operating system?
Recent Mac AND Windows operating systems have been known to cause "odd" problems
Are you using a computer Administrator account with full read/write permission?
If you have a Mac with El Capitan or Sierra, or a PC with Windows 10, your old program is not compatible