Hi, I recently bought a Macbook pro a1278 2011 (intel core i5, 4gb ram) from one of my customers (i run a computer repair business). The problem i am having is that the left click doesn't work although i can move the cursor as normal. (As a note the dvd drive spits out most dvds after a few seconds and the Mac book seems a bit slow.) with the track pad disconnected an external USB mouse works fine but when the track pad is connected i can only right click with the external mouse and track pad but still move the cursor as normal. I have tried the following: a brand new hard drive - total of 2 hard drives tried. Re-installed os x 10.7 several times from known working install DVDs and from the internet recovery. Replaced the track pad (same issue on both the old and brand new track pad). Tried with out the battery. Turned blue tooth off and i do not have a wireless, Bluetooth or apple mouse. Reset the SMC. Reset the PRAM and NVRAM. Tried with the dvd drive disconnected. Tried installing all updates. Tried with the battery removed. I tried to preform firmware updates but the installer said it was not supported (i have triple checked i had the correct version) Tried installing all available updates. Tried holding the power button for 3 minutes with the battery and mag safe removed. Tried new known working memory. Tried one stick of memory at a time in each slot. Tried repair the disk and permissions in disk utility. Tried looking in system preferences and playing with the settings (tap to click is enabled but i have tried with it disabled.) I have tried creating new users both standard users and admin users. I have loosened and tightened the screws holding the track pad in place. Tried different mag safe adapters and running off the battery. Tried reseating and with the keyboard unplugged. ( i dont know if its normal or not but i lose keyboard functionality when the track pad is unplugged.) Tried with the track pad not screwed in. I am trained as a windows pc repair technician and dont have that much knowledge about macs. Many thanks in advance any help will be massively appreciated.