is this xp?
click start/my computer right click your cd drive/properties and select autoplay.
from the drop down box select an action to perform when you insert different types of disc.click here
for win 98 i think you do this click here
if that does not work and if its xp then you can enable autorun in the registry,to do so click:
start/run type regedit and click ok.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\CDRom you will see "autorun" on the right,click it and set the value to 1 to enable and 0 to disable.restart the computer.