I had somewhat the same problem. My touchpad is an Alps multitouch ( Acer Aspire 7741G ). Sometimes, either after removing usb mouse or after resuming from suspend (can't figure out exactly which one, but I think one of these 2), my touchpad would stop working. I tried most advices (psmouse, xinput, etc), none worked. Logging out would make the touchpad work, but only for the login screen, after logging in, it would stop again. Reboot did not help either, same as log out.
while contemplating reinstalling ubuntu, I tried logging in with the guest account. The mouse worked after login! So I started wondering if somehow my account settings (kept in the .xxx dirs/files in your home dir - you can see them with "ls -a" command, like ".config") were at fault. So i did a backup of all my hidden dirs/files, and deleted them all (at login, if they are missing, they will be recreated, and you will have the desktop you had after installing).
And it worked! I didn't figure out exactly where the wrong settings were, but I suspect that it is someting like ".config/unity". If you don't want to lose all your settings (browser, transmission, unity, etc), you can try making a backup and deleting sequentially until you find the source, after that restore the ones that had nothing to do with the problem. I had no patience and deleted them all and had to redo all settings (too lazy to copy from backup).
Hope this helps somebody!