Few more details required:
1. GPU model?
2. GPU temp's while gaming?
3. Are you running the latest GPU drivers?
4. When does the problem happen....does it happen immediately on startup of the game or after a while of gaming? Could be a heat issue.
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.
Albeit the GPU is hot, you may want to check your CPU temps also. it definately sounds like the case has insufficient cooling. If you can play with the case's side cover off, it's definately a heat issue.
If it were the processor it would be shutting down on more than just games. I hope 41 - 84 temp is for the GPU as those temps are certainly high for a CPU to the point it should throttle, then shut down. It sounds like you just have a heat issue.
The processor doesn't seem to be the issue. As Hawkeye22 said, if it were then it wouldn't be happening only while running games. I'm quite certain its your GPU.
While you were playing with the side panel off, did the machine shut down again?
84 is still pretty high for your GPU. You should double check that it's the GPU temp only! If it is, you may have a faulty GPU. See if you can return it for a replacement?
I would recommend installing another GPU (if it is possible) and running the game again. I know people usually don't have spare/ better GPU's lying around collecting dust, but like I said, 'if possible'. Because that would certainly point out the problem.
How old is your CPU? Is it within warranty? If so, look at returning it and getting a replacement. If not, well, it's not a bad idea to upgrade your CPU. The upgrade, if any, will depend on your motherboard model number.