Download and install the Mac OS X 10.5.7 Update, or later.
If you're not ready to update, you can avoid this issue in Mac OS X 10.5 through 10.5.6 by not moving your mouse after you click the Log Out button, until the login window appears.
You can also restore the mouse pointer's movement by logging in and logging back out via the keyboard in Mac OS X 10.5 through 10.5.6, as follows:
- If a list of user accounts appears in the login window, use the Up and Down arrow keys to highlight a user account's name, press the Return key to select the account, type the account password, and press Return to log in.
If the login window is set to display a Name and Password field instead of a list of users, type in a user's name, press the Tab key to navigate to the Password field, enter the user's password, and press the Return key to log in.
- Log out using the keyboard (press Command-Shift-Q, then press Return). The mouse pointer should respond.