Reinstall your sound card drivers. Could be that your sound card has been shorted out, which could happen if you are plugging in speakers while the computer is on. It could also be that your speaker have shorted out. Plug in headphones or another set of speakers to see if the sound is still garbled. If sound is clear with other speakers or headphones, then you know the speakers you were using are bad.
Most sound cards come with a little program that will let you set different
sound effects and that sounds like what you have done. Look for the program
in "programs" and set it back to normal.