how do i change the cord in my bathroom light, do i need to buy a new light?

Firstly. Turn off the main circuit breaker in the distribution box and make sure it stays off. Unscrew the outer casing of the ceiling switch. If possible retrieve the pull-knob from the broken cord. Depending where it broke, you might be able to re-use the cord, otherwise get some nylon woven cord, pass it through the hole in the bit you unscrewed and fit it to the switch (Usually needs a double knot). Refit the casing, and then, and only then, turn the mains back on.

Jim
January 2011