Cannot boot vSphere ESXi 5.0/5.1 server from HDD

Hi,

I just installed a new ESXi server (2 cores CPU, 2x1 TBytes disks). The installation was done in the version 5.0 (because I needed to convert previously existing VMware Server 2.0 machines) and than upgraded to the version 5.1.

Neither in 5.0 nor in 5.1 the server cannot boot from HDD ("Please insert bootable device..." after about half a minute). I need to boot from CD and than to select "Boot from local disk" option.

I hope there is an option to configure boot from HDD normally. Any suggestions haow to do this in vSphere ESXi 5.1 server?

Thanks in advance,

Ilia