My hp pc seems to try to start on but then it shuts down immedia.

Do any of the fans plug into the wires going directly to the power supply? If so, you probably have a bad power supply. If they all plug into the motherboard, it could be the motherboard at fault, though usually when something fails because of the motherboard, it can still tell you what it was via beep codes and such. I would think the power supply is to blame, and the upside is that they are cheaper than the motherboards if you are interested in keeping this PC for a while longer.

Hi there.
If its the CPU (processor fan) thats not working, it could well be the machine overheating and shutting down to prevent further damage to the machine, try another fan, if it spins up the CPU fan has gone and will need to be replaced.
If you have a working fan but it doesn't work on the motherboard, check the power supply unit as that could be faulty.

Good luck and thanks for using FixYa!!