exchange 2k instalation error!

I Recently reinstalled one of my servers (clean install) and then named it the same name as before. this server used to be a DC and now is one too.
when i want to install echange 2k on this server i get this error message
“A server object for thisserver(“My server name”) Already exisit in the administrative group “first administrative group”. you must eaither remove this server object before installing or run setup with setup recovery”

i need help removing this object, i don’t know where it would be.

thank yuu