I have prime rib steaks that I put into marinade 7 days ago and forgot about them. Are they still good to eat?

pegeen 100% right. The only solace is knowing that we all have had our own version of that blooper in our cooking lives!

Definitely no. So sorry since it's prime rib, but you should throw out the meat and the marinade right away. Wash the container in the dish washer or pour some boiling water and soap over it. The storage guideline for refrigerating that type of meat is 3 to 5 days at a temperature of 40 F or lower. (You'd have to check your fridge setting: not everyone has their fridge set at 40 F.)
http://www.foodsafety.gov/keep/charts/storagetimes.html