Does the pressure increase when you backwash? Try putting the valve in recirculate (this bypasses the filter)and see if the pressure changes. If not you have another problem. If it does change the sand....

Thank you, we will change the sand.

You might also find that the pump impeller is fouled with debris. This can happen quickly, especially if the pump was operated for even a short period of time without the strainer basket in place.
The impeller can also be eroded from cavitation if air is getting into the system (usually from the skimmers).

Hi,
Sorry took so long to get back--we took the filter out--
the sand had a layer of thick gray gooey stuff on top.
Hubby figured it was algae. We changed the sand and
all is good.
Thank you for your answers.