>an error message
Just guessing, since you provide zero details, but I'd say your computer is too old and weak to run video editing
Come back with details, and someone may be able to help
Need to know all of your computer hardware, and all other software that is also running
I'm with John. The main reasons the program won't launch are:
1) Inadequate hardware. You should have at least double what Adobe lists as minimums. In particular, you'll not only need room on your hard drive to install the program but at least 20 gigs of free, defragmented space just to open it. (It's not that the program itself requires that much. But your operating system needs lots of paging space to run more intensive programs.) You'll also need two or three times that free space to do any video editing.
2) Outdated firmware. In particular, and outdated version of Quicktime. Your Windows Update doesn't always load all the necessary updates. Secunia's program can help you find out what else you need, per the FAQs to the right of this forum.
3) Finally, there is the possibility the program didn't take on the first installation. Occasionally, when your system is updated and you have adequate hardware, you may need to uninstall the program and reinstall it to get it to run right.