When pegs become seriously worn see your local professional repairman. Your bow hair has tiny teeth which, with the help of rosin, grip the strings and pull the sound out of your instrument. With use, the hair's ability to grip the strings and pull a beautiful sound is reduced. The result is a scratchy, harsh sound. Have your bow rehaired at least twice yearly, more often if you play many hours a day .
Grooves prohibit free vibration of the strings.
Be sure the board has a sufficient concave dip. See your repairman. He will also check the grooves in the nut. They may be worn too deep. In warm weather the tops of many cellos tend to swell upward.