Try a repair of your Avast installation, via the control panel, add/remove programs (or in Vista, programs and settings.)
The area you refer to (bottom right) is called the system tray, or "systray" for short, and the Avast icon should indeed be there.
If you open taskmanager, is ashServ.exe present?
Now the real question is why did he have to disable Avast to install or use this Pinnacle Studio?
Perhaps it is a non-legitimate copy, and contains a malware file. I would be very suspicious of that. Did Avast alert to any malware while this program was being installed or run? If not, why disable?
From where did this Pinnacle studio come? (Download site, please, if applicable.)
If so, what is the name and path of the detection, please?
The other possibility is that it is a false detection (these happen, occasionally) and steps can be taken to put it right.