rpm got stuck

[Nina Pham]

I was intalling some rpms, then it got stuck. I follow the instruction 
on the internet to delete the db files for rpm, and rebuild. So I 
deleted rm -f /var/lib/rpm/__db*, then
#rpm -vv rebuilddb
waring: waiting for transaction lock

and stuck there, so I do Ctrl_Z to exit. Then Do rpm -e  
kerio-mailserver, get the same warning, and error can not create 
transaction lock.

Do you have any idea what happened? and what I need to do to fix it?