Is there an easy fix for this problem, or do I need to call a plumber? My toilet won't fill with water.

Is it your tank that doesn't fill or your actual toilet bowl? The tank should fill to 1/2" short of over flowing at the white tube in the tank. If it doesn't adjust the float until you get that level. If the toilet bowl doesn't fill correctly check to see if your fill tube goes into the over flow tube correctly. Back to you.

Tank or bowl? I'm going with tank. I'm putting up two images, which ballcock do you have? Back to you. Tom