Cleaning an audio file

I have recorded plenty with my olympus vn5200-pc but this last time if fouled up when I recorded class lecture by recording very faint with a strange constant noise.. I wonder if I can amplify and clean it up in an easy manner.. I tried audicity but improvement was very minimal ( i know that program minimally and just used the amplify and naturalize functions)

any input is appreciated.. format is .wma and length is about 1 hour.

Possible Yes, Easy No.

You should be able to remove a hum of say a motor or air handler unit with high and low pass filters. This probably won't be automatic.

audacity noise removal requires the user to find a continuous noise-only segment and the software will establish a noise profile from that segment. It is different from the "special sound effect/plugin" function.

It actually works pretty well. Details are in
http://wiki.audacityteam.org/wiki/Noise_Removal