My well pump will prime , but as soon as I open the valve to let water into the house , the pump will loose prime. Please help

What kind of pump? Is it a jet-pump? Deep or shallow?

I don't know a lot about jet-pumps, I have submersible and you don't prime those. A guess (and it's a guess!) could be that you're not getting a full prime... i.e. there is still air in the pipe between the water level in the well and the pump. This could be caused by a faulty check valve.

Good luck!

~aaron