the yellow exclamation mark is telling you that the USB drivers for your mouse are not installed, if you have an install disk for the mouse, try putting it in and see if it autoruns, that might allow you to install the needed drivers and setup the mouse. windows98 does not have native usb drivers, you need to install them for the items to work.
try unplugging the mouse before putting the cd in.
ps, a typical USB connection on a mobo has 9 pins, 5 on one row and 4 on the other.
the extra pin is not used so dont try searching for a missing wire.
red, yellow(or white), green, black is the correct taken from left to right. at least it is on mine.
hope this helps, good luck