No parameter values (e.g. rate constants, mass transfer coefficients, heat transfer coefficients etc.) have been given. If values aren't given to parameters, a value of zero is assumed, which can cause rates of reaction, mass transfer etc to be zero which results in flat profiles.
The correct profiles are not being plotted or are not being shown due to axis scaling. Check the legend for profiles that should vary, and rescale if necessary using the arrow buttons on the y-axis.
The incorrect end time was specified. Check the units of time on the x-axis and also the end time. If the end time is too short, then it is likely that no significant change was observed over this short period. Correct this either using the continue function in the solver options panel, or in the model data sheet.
The simulation converts all reactants into products in a very short time (i.e. profiles look flat because all profiles are parallel to the y-axis). Use the x-axis controls to zoom in on results for very short times, or look in List all phases at the early part of the simulation. This behavior normally results from setting very high rate constants or species concentrations, or allowing temperature to rise without imposing its profile or cooling the phase.