What are the steps if ESX not booting ?

1. Make sure that the cpu on the host supports VT (can be enabled in bios) and has 64 bit capabilites.
2. If booting from SAN LUN and LUN connectivity have issue ( in HBA, FC, Switch, SP ).
3. If installed locally then may be disk problem or OS corrupted. Take out the disk and install it on other machine as secondary and primary and check.
4. If any new hardware or s/w installed then remove that.
5. Giving any error on screen or purpole screen error.
6. This issue occurs if the esx.conf file is corrupted.

To repair the file:

1.Select the Troubleshooting or Service Console Only boot option when the GRUB bootloader appears.

2.Log into the terminal as root.

3.Run the commands:

esxcfg-boot -p

esxcfg-boot -b (ESX 3.x only)

esxcfg-boot -r (ESX 3.x only)

4.Reboot the ESX host using the reboot command