HPProliant D L 380 with Windows Server 2003 problem

Hello there!
I got a little problem…
We are using the HP Proliant D L 380 as server. And the OS is Windows Server 2003 Professional.
It have implemented one year back and some days before accidentally I deleted the ‘hostname’ in Server.
How can i retrieve or back it again…
Somebody please help me…
Thank you…
