HP does not have the 8640p model. Are you consulting the 8460p notebook?
Upon inquiry, this notebook has not passed the test of i7 36 10QM cpu, so it can't be guaranteed to work normally after installation.
If this type of cpu can't be turned on normally after being replaced at present, it means that the cpu is not supported and refreshing the bios can't solve it;
So if you want to upgrade the i7 series cpu, please refer to the following information:
Intel Core i7-2720QM processor (2.20 GHz, 6 MB L3 cache, 4 cores /8 threads, 45W)
Intel Core i7-2630QM processor (2.00 GHz, 6 MB L3 cache, 4 cores /8 threads, 45W)
Intel Core i7-2620M processor (2.70 GHz, 4 MB L3 cache, 2 cores /4 threads, 35 watts)
I hope the above reply can help you.