Cannot open Terminal on mac ("Not allowed to use" error message)
Your best bet would be to do a clean install, presuming you have copies / licenses for any software you use on there. Backup any files you want to keep, and follow one of the many guides out there. For instance:

http://mashable.com/2015/10/01/clean-install-os-x-el-capitan/

This could well take less time than figuring out what the IT guys did, and make your Mac faster in the long run.