Change the sample rate back to what it was. You didn't specify whay program you were using, but what you WANT to do is "resample" the song at a new rate, not "change" the sample rate.
By "changing" the sample rate you are merely changing the rate at which the data is presented to your sound card. (As you found out). By "resampleing" the data with a new rate, you literally "reprocess" the song with a higher rate.
Unfortuneately this will NOT do what you want anyway. You can't make a poor sound any better just by jacking up it's sample rate. It doesn't work that way. It's kind of like when you take a picture from the web and double it's size in a photo editor... the picture becomes "pixelated" and looks like crap.
What you'll need to do to get a nice clean sound is re-record the tracks. You need to ask yourself if it's:
A) Worth it?
B) Necessesary?
Oh yeah! I never tried this myself, but I heard a friend tell me that he "resampled" a track with a higher rate, then copied the track (doubled it); offest one of the two new tracks by like a couple hundredths of a second then panned them out about 45 degrees from eachother... he said it made it sound much fuller and overall much better. Might give that a try before scrapping anything.
- Tanlith -