Windows does not detect a mouse.

On boot up “Windows Mouse Support” window appears with the message “Windows did not detect a mouse attached to the computer”. Although the mouse is plugged in.

This has only just occurred as there was no problem with the mouse before but now only the keyboard can be used.

The system is running on Windows 98 and I have re loaded the operating system. Have checked the physical connections and tested the actual mouse on another machine.

What has caused the machine not to recognise the mouse and how can I rectify the problem?