[ubuntu] touchpad not working after update on 11.04, Acer aspire 5542g

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http://ubuntuforums.org – hi there! I had Ubuntu 10.10 and I updated it to 11.04. Now touchpad isn't working :( it works well on log in screen and I can click on my username and move it but when I click log in it freezes and can't move mouse using it or click left or right button. can you please help me? I'm using Acer aspire 5542g and 64-bit Ubuntu 11.04. thanks and sorry if thread like this already exists (Hardware)