First, you should not have both installed. It is not recommended nor supported.
Second, hat do you mean by "activate"? You would "activate" Adobe Acrobat after you purchase it and have a serial number.
At any rate, if the trial isn't working, whether it wants you to activate it or if the trial is up (yes, that can happen immediatly under some circumstances), you might as well uninstall it. The only way to get it working again is a complete format of your hard drive.
If you uninstall it, you may have to do the same with Reader then reinstall it to get it working again.