I had this problem as well. Apparently, Examsoft turns down the volume so that the noise won't interrupt other test takers if your computer reboots during the exam. I know you fixed it already, but for future readers, it's pretty easy (at least on a PC). Go to Control Panel/Sounds and Audio Devices. Under Device Volume, click on "Advanced." Move the bar up to the top, and click out.
(Thanks to the IT department at, I believe, the University of Iowa for putting this up online so I didn't have to deal with bringing my computer into IT.)