The fan speed control system is set to send out a signal to the fan that never takes it below a certain power setting, or it may stall. If the fan starts and runs fast for a few seconds and then stalls, you may have worn bearings on the fan. Now, if that does not work, you have another problem. Check that the BIOS Setup screens now DO show the fan as detected with a reasonable speed, and NOT stopping. If it fixes your problem, you can close up and continue.

What this does is 'scrub' the surfaces of the contacts in the connector and header to clean them, re-establishing a good electrical connection. Did the fan start fast right away? Normally it will, and then in a few seconds it will slow down but keep going. Leave the case cover open so you can see the fan and reboot. Check to be sure it is reconnected AND you did not loosen something else. Shut down, open your case, and find the connector for the Wraith cooler where it plugs into the mobo CPU_FAN header. It is based on the possibility that a small amount of dirt or oxidation of metal contacts may have produced a poor connection. You just need to be careful when moving things that you do not dislodge something else. Try this simple trick I use often, and it's free.

Amd wraith prism fan control