After installing a recent software update any USB devices that worked before no longer appear on my desktop, meaning that I am unable to use them. The ports seem to work, my keyboard and mouse are both operational. I have checked the System Profiler and the computer seems to be able to detect any connected devices. I just can't use or open them as they are not shown on the desktop. My Mac has worked perfectly (as I expected) ever since I bought it, so this kind of malfunction really surprises me. Any help would be appreciated. Thanks.