Sensible,
It would help knowing a little more about the hardware you are running. If your mouse is connected to the PS2 Port, I would turn the computer off, and then make sure the plug is fully in to the PS2 Port. (It would be worth completely unplugging it and plugging it in again.)
If your Mouse is on the USB Port then it could be another problem. Since USB is a hot plug you could try unplugging it from the port and plug it in again while the computer is still running.
There is always the chance the Mouse failed.
Take Care,
Richard