Mouse and Keyboard lock in Safe Mode

Whenever I boot my Dell Dimension 3000 in Safe Mode, my mouse works fine until a press a key in my keyboard. When I press a key in my keyboard, the mouse and keyboard stop working. I'm sure that the operating system works fine because when I press the power button to turn off my computer, I receive the message "your computer is shutting down..." Can anyone please help me with this problem? It only happens when I boot in Safe Mode. Normal mode works fine.