I installed CoolEdit 1.53. recorded some noise, about 5 seconds worth. Clicked from the Transform menu the Noise Reduction effect.
When the dialog box opens the ability to apply Noise Reduction is grayed out. Which apparently this is what your seeing.
Now what you should do, (unless you are doing this and its still not working then reply back), but at this stage, with the NR box open and grayed out, you should next, click the Set Noise Level to gather the information about the noise you wish to reduce.
After that runs, the Noise Reduction effect will close. You'll see your waveform window again.
Now, go back to the Transform menu then select Noise Reduction again. This time, the box should have your noise profile and the OK box will be useable. Adjust the slider to the amount of noise reduction your wish to apply. Click OK.
If you plan to apply the same Noise Reduction to a music collection, you may want to create a noise profile that your can quickly apply over and over again without going through the discovery process.
I would do this before recording anything. Create a Noise Profile of the computers internal noise, line-noise, AC 60hz humm, DC noise, Fan Noise, general electronic noise. Unless you happen to have a very electrical clean system. But most people wont as eliminating this type of electronic noise from a computer can be costly.
If the above does not solve your problem after trying it, then reply back with your results.
Also, as your using an older version of a CoolEdit with crippled effect. I have written a Howto on this board to gain ALL effect and still be legit.
To add further, you could always try a great Freeware editor, Audacity, which is what I use today, as I can use it on my new Dual-Core Mac's and my Slackware machines and my MS Windows boxes. It's got plenty of features and its completely freeware.