And does it do this when you do not had the external drive plugged in?
Have you run the search tool on the drive so that it indexes it fully? It could be that searching is simply taking too long because of no index.
Could be something else, could be your USB port - have you tried another USB port?
Is the WD powered properly? can you provide power to it from a PSU or phone charger to see if it's your USB port not providing enough power?