Windows 2000 Professional Freezes

Whenever I restart my pc it freezes. What I mean by that?s if I press restart it shuts down OK but won?t start up also when my pc is shut I am not able to start it unless I turn the power plug off and on.

This problem started after I have replaced my cdrom with a cdwriter. I also noticed that I have my network card and sound card sharing the same IRQs #9 on device manager.

Please advice. Thanks in adv.