Check the following:
1. you should do DNS name resolution successfully: When you want to open with FQDN, the client must resolve the VCSA IP address
2. Try to open VAMI: http://VCSA_IP_ADDR:5480 and if you could check all the services status
3. Check the firewall settings of your web client's system. (or even antivirus built-in firewall, if you have)
4. Change your browser and check the system proxy settings
5. Check time setting of the client system and vCenter server.