Definitely a heat issue! Those temp's are way abnormal for your 5450, that's what is causing the shutdown. Couple of things you can try:
1. Remove the side panel and point a small fan directly at the card. Try and get the ambient temp's down (like, using an aircon if you have one in the same room as the comp)
2. Heat issues can also be related to the case being used. Make sure your case is well ventilated. Sorry to say, but two fans won't cut it for you. If possible, get another one and make sure it throws the air 'outside' the case.
I'm also beginning to wonder if your GPU is faulty. Do you get this issue with other games as well or only NFS HP? That card shouldn't run so hot. If the problem persists, do not run the game(s)....that could (and would) fry your GPU! If its a faulty card, you could RMA it, provided its within the warranty. Try out some other games first, just oto be sure.