I have freshly installed ESXI 4. But when ever i reboot my server all the setting gets lost like IP setting move back to automatic instead of static, the license key gets lost.
Given 4i takes about as long to reinstall as it does to post a question on SF.com why not try reinstalling from scratch.
I've had this problem a few times when running it from a USB key. Usually it's solved by tinkering with the memory / advanced settings.
I've never actually found the direct solution but after adjusting the VM memory reservations it seems to remember it and then remembers the other settings too.
Also try enabling the SSH server or going onto the system console and writing to the configuration disk to verify that is possible.