I have the same problem. I even tried contacting Microsoft, but they are not aware of the issue.
It seems it's a driver incompatibility. Windows 8 can't detect the inbuilt webcam, its hidden after sometime using the laptop. And when you scan for hardware changes, it won't be detected again, with an Error Code 45.
I don't know if Acer will ever release an updated Chipset driver, because according to Microsoft, it might fix this issue.
What I did is perform a "Refresh my Windows" but I didn't work. So I searched again and saw this method; I uninstalled NVIDIA driver (one forum says, this causes the issue), shutdown the notebook, remove the battery. Hold the power button for 30 seconds and leave it overnight. They say it releases static build up due to the driver conflicts.
After I went home from work. I booted my notebook. The "Imaging Device" tab is present again. HD Webcam is installed, so far so good. So I thought it was fixed. I proceed to install my programs (due to the "Refresh" thing). But after a reboot. The HD Webcam is missing from the Device Manager again.
I contacted Microsoft again. They say that I should disable the NVIDIA driver, cause that's what I told them, that in one forum this causes the issue. I did that but to no avail. The HD webcam is still not installed nor detected, I've uninstalled even my security software case I thought it also causes conlicts. But it didn't work too.
I don't know if its a power issue too, but I think its mostly driver incompatibilities. I'm still trying to fix it though.