Software Centre Freezes often in Ubuntu 12.04 LTS 64-bit

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http://askubuntu.com – Whenever I try to install any add-ons of any software(Kile, Lyx etc) in Software Centre, it stops to respond and the screen gets dark. I'm using Dell Vostro 1450( i3-2330m, 4GB, 500GB) and 64-bit Ubuntu 12.04 LTS dual boot with Win7 prof 64-bit. Why this happens,and what to do in this situation, pls answer. (HowTos)