It's very likely that your PS4 just has a broken HDMI port. The ports on these are very fragile and break often. Many times you will still be able to hear sound even if you don't see a picture. Since your PS4 starts up normally and everything seems to work fine other than you don't get a picture there is most likely nothing major wrong. It's very, very likely that it's just an HDMI port issue.
When he jumped on it he probably either jumped on the HDMI cable or somehow caused the cable to get jammed into the port. This could have easily caused it to go bad. The original HDMI ports on these were really bad.