I have a bit of an odd issue that I am hoping someone in the community can point me in the right direction on.
Background: We have an older ESX host that is not part of our primary production ESXi cluster. It is mostly used for putting up test machines and other non-essential activities, and I have been asked to upgrade it to the most recent version. It is currently running ESXi 3.5. Rather than try to do sequential upgrades from 3.5 to 4.x then 4.x to 5.1, I decided it would be simpler to just do a fresh install of ESXi 5.1 and import the VMs afterward (I exported them out with VM Converter beforehand).
Problem: The install itself for 5.1 seems to go perfectly fine. I boot from the install disc, it detects an existing VMFS instance, which I tell it to overwrite, and the installation continues on its merry way until it completes and says it would like to reboot. However, after rebooting, the server goes right back into the old 3.5 version, with all the old settings - as if I hadn't done the install at all.
I'm new to ESX/ESXi and not sure what to make of this. Any guidance would be most appreciated. 