Here are few things you should try:
I am assuming you are trying a local mode test:
1- Make sure you have VM's with the prefix BIO in datacenter that was mentioned while adding vCenter.
2- Check Infra Server test is successful in "SERVERS" tab.
3- Make sure view planner agent is installed in desktop and you can see agent command window when logged in, and there is no error reported in agent command window.
4- Check if autologin is enabled in desktops.
If above does not work, reply back with test details (run mode, windows version, Horizon version and http://<HARNESS_IP>3307/vpresults/<RUN_NAME>/harness_run.log file.)