With a laptop, if you don't hear the fan, I suspect that it actually is NOT running -- and that is a serious issue as your PC will overheat almost immediately and shut down as a result.
That being the case, you need to get the fan replaced and such repairs can be very difficult and risky to perform, depending on how much stuff has to be removed in order to get to the fan to replace it.
For such repair estimates, you would need to contact an HP Repair or Service Center.
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