Knocking

What is your question?

Just bought this car 3 weeks ago its in great shape, has a 115,000 miles on it, yesterday while on the highway while i was trying to pass someone i noticed i didnt have any pick up to do i looked down saw my oil pressure was in the red pulled over and my car died, wouldnt turn over or anything i replaced the alternator, the battery and gave it an pil change it started right up now there is a knocking and it does not pick up when i step on the gas i have no juice any ideas?