Move your cursor around your screen and look at the icon that appears. The selection tool is the default tool and features an icon of an arrow. However, if an icon other than an arrow appears, you may have accidentally switched to a different tool.
Find the tool panel, often located in the upper left hand corner. Depending on how you have your screen organized, the tool panel could be in various places on your screen.
Click on the arrow icon on the tool panel to set your default tool back to the selection tool.
Press the "V" key on your keyboard if you can't find the tool panel. The "V" key is a shortcut to set the selection tool as your default tool.
Press "control" plus "alt" plus "delete" on a PC if your computer is not responding when you try to click on the selection tool. Press "command" plus "option" plus "escape" on a Mac if your computer is not responding when you try to click on the selection tool. If your computer is not responding, it may mean your computer is frozen. These cues will force the program to quit and allow you to restart in a fresh mode. Be sure to periodically save your project as you work so that you don't lose what you have accomplished.
Call Adobe Support at 800-833-6687 Monday through Friday if you are still having problems with the selection tool to speak with a representative. (See Resources)