Hard to say what happened. How does your hardware look like? Since you say the HDDs are not detected but you are still able to boot, I assume you are booting from USB!? How many disks do you use and what kind of disk controller. Which version/build of ESXi do you use and was the oem.tgz you used to replace the original one built for exactly this version?
Even though this may not be an option at the moment, I strongly recommend not to touch the installation just because of adding a NIC driver. You can get a known as working NIC (e.g. Intel Pro/1000 GT) for ~$30.
André
