The problem is that the PS/2-style mouse and the serial mouse are not just different in terms of the connectors they use, they are different electrically as well. The signaling levels are different, so just using an adapter will not always work. What complicates the matter so much is that there are some mice that are called "combo" mice, which will automatically use either the PS/2 or the serial signaling depending on what sort of system they are plugged into. This type of mouse, when used with an adapter of the sort mentioned above, will work in a serial port. However, not all PS/2-style mice are combo mice, and this is what causes all the confusion. To make matters worse, most mice do not have printed on them whether they are "combo" or not, and sometimes even the documentation is not very helpful. (Buying a mouse with a PS/2 port that comes with a PS/2-to-serial adapter is a good hint that it is combo, of course!)
· Check the instructions that come with your mouse to find out if it is a combo mouse. If it is, then it should work with the adapter. Make sure the adapter is tightly fitted to the connector and that there are no bent pins or other physical issues.
· If you don't have a real combo mouse, or aren't sure if you do or not, then try borrowing one from another PC and see if it works instead.