ITU's main support page is here. For general GMU lab, networking, or computing facilities issues, you can contact ITU Support at (703) 993-8870 or send email to support /@/ gmu.edu
IT&E maintains a website with information on the IT&E labs, resources, and policies. It's quite handy. You can contact them with IT&E-related problems at system /@/ ite.gmu.edu
For specific problems with the CS clusters or CS accounts, send email to help /@/ cs.gmu.edu