Newly installed GFI will not reset?

I replaced a standard outlet with a GFI outlet in an older kitchen, a 12-2 w/ ground fed the box. At the same time I added an additional unprotected outlet for a dishwasher down stream. Both black wires hooked to side with dark screws, and both whites to light screws. Both grounds twisted and connected to green screw. Powered up and it tripped and will not reset unless power is off. I checked the downstream outlet with a 3-light tester, and it shows that it is wired correctly. Where do I start?