24 hours is too soon to worry. Although you can't see anything, most likely the yeast are multiplying like crazy. They'll start fizzing as soon as they are ready.
What temp is your fermenter at, and what temp did you pitch at? Did you rehydrate the yeast before pitching? How (if) did you oxygenate the wort? These things can make a difference to how quickly your fermentation starts, but it will start eventually pretty much whatever you did.
My last brew took over 24 hours to kick off, I think mostly because I was keeping it cool. It was going strong 48 hours in, though, and still chugging slowly a week later.