[ubuntu] Left mouse click not detected

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http://ubuntuforums.org – I had Ubuntu 12.04 with XFCE (Lubuntu) installed on my Acer netbook for a while until one day the left track pad button stopped working. For unrelated reasons, I wiped it clean and installed regular old Ubuntu 12.04 and attached a USB mouse (that I know to work). To my surprise, I still wasn't able to left-click. I also enabled touch click on the trackpad, but this didn't help either. I tried changing window managers to no avail. xev does not register any click at all. I've seen this issue discussed a lot, but it's usually in the context of an older version of Ubuntu or with an HP button-less (Hardware)