My mouse doesn't work right in my ibook g3 12inch 900 MHZ

Hi,

I'm having trouble getting a mouse to work using the usb port. The mouse will light up but it won't move the cursor. The track pad works with out any problems. I've looked at the mouse settings in system profile but can't find any problems with the settings. I'm assuming that when you plug a mouse in the usb port it should over ride the trackpad. I could be missing something that I need to do in addition to just plugging in the mouse. Recently, I'm also notice that I can no longer double click on the trackpad to open an application. I have to tap once to highlight the app then go to the toolbar and use the scroll down menu to click open in order to open the app. Does anyone have any thoughts as to what my problems are? Thanks, appreciate any help.