The fact that you were able to install ESXi proves that the network adapter has been detected.
To start with troubleshooting:
- check the physical connection/network cable
- ensure the IP address/subnet mask you assigned is correct (no typos) and the physical switch port is configured properly (e.g. access mode, correct VLAN, speed/duplex...)
- run esxtop (press 'n' for network) from the ESXi hosts shell to see whether it shows traffic on the network adapter
André