USB mouse not working upon bootup

[yy]

Hi,

I'm using Dapper and I'm having some problem with my usb mouse. After 
booting up Ubuntu and reaching the login screen, my mouse does not work 
i.e. no matter how I move my mouse
the mouse cursor does not move. After plugging the usb mouse out and 
plugging it in back to the same usb port, the mouse mysteriously 
responds. If I do a reboot, the mouse will also work.
However, if I do a cold start, the mouse always does not seem to work.

Can someone advise me on what's causing this strange behaviour? Any help 
will be greatly appreciated!

Regards,
YY