I chose to graph confidence or prediction bands with nonlinear or linear regression, but they don't appear on the graph

Prism will not plot confidence or prediction bands in several situations:

• If the best-fit value of a parameter hits a constraint, the fit is unlikely to be useful. Prism does not plot confidence or prediction bands, because they would almost certainly be misleading.
• If the results of nonlinear regression are ambiguous, the confidence or prediction bands would be super wide, maybe infinitely wide. They would not be useful, so Prism does not plot them.
• If you choose robust nonlinear regression, Prism does not compute confidence or prediction bands, as it cannot compute standard errors or confidence intervals of the parameters. 
• The fit is perfect. If the sum-of-squares is 0.0 and R² is 1.0, it is not possible to compute or interpret confidence or prediction bands.
• If the fit is interrupted, confidence and prediction bands are not computed.