[ubuntu] internet and video lag

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http://ubuntuforums.org – I have just installed ubuntu 12.04 with cd, manually, means, I made an ubuntu partition alongside windows, I made a 2.5 GB Swap partition (because I have 1.2 GB of RAM), I have a second hard disk drive of 10 GB and I made that to my home folder. everything works perfect, but, there is always a "but", I tried to play a 5 minutes HD movie, which I made by myself, and it displayed just a white screen and played the sound. I fixed that almost by inputing into terminal Code: sudo apt-get install ubuntu-restricted-extras but it still lags and every 5th picture is blank then (Hardware)