A lot more detailed, complete and sensible information is needed before anyone can help you. There are no mind readers or clairvoyants here. Platform (Mac or Win), exact version of the OS and of Photoshop you are running (CS5 what? e.g. CS 5.1 version 12.0.1), complete hardware and software details, etc.
Please read this FAQ for advice on how to ask your questions correctly for quicker and better answers:
Above all, what error message are you getting, and are you trying to use the auto update?
For any version up to CS5, the Adobe auto updater is most unreliable. You'll have to look for, download and installed the updates manually yourself, following the instructions on the download page to the letter.