If the first part didn't fix things...
RIGHT click on Start, choose "Explore". When that loads, click on "View" in the upper left, then choose "Folder Options" from the menu. When that loads, click on the "File Types" tab at the top, then scroll down to the "AudioCD" listing, then click on it once to highlight it. Look at the bottom section and it will tell you which program is supposed to open when a CD is playing.(It should say CDPlayer, or something similar and you should now do a "Search/Find" for that file name, just to make sure that it is still on the computer and you need to identify the path to the player.) Next, click on the "Edit" button. When the "Edit" window loads, click on the "Play" listing in the white "Actions" area to highlight it, then click on "Edit" below it. When that loads, look to see that the "Action" area at the top lists "&Play". (it will be greyed out and can't be changed.) Then in the line below it titled "Application used to perform action", it should say something like this: "C:\windows/cdplayer.exe /play". (The "cdplayer.exe" section could be slightly different on your's, but most Win98's have this particular program as the default CD player.) If it doesn't list the line correctly, edit the line so it displays the correct path to the CD player and make sure the /play is at the end of the line, leaving a single space between the .exe and the forward slash.
Now do the same thing for the "CD Audio Track" listing in "File Types".(If its there.) Make sure the same default CD player is listed and the entries are the same for /play.
Hope this helps and let us know how it goes.
Grif