ubuntu software center is frozen doing the cancel process

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http://askubuntu.com – When I was using the software center and trying to install flash, I thought it was frozen and so tried to stop and restart. Then it got stuck at cancelling for about 2 hours. Is there a way to manually stop the cancel process I've tried rebooting and still no luck please help me as while it is frozen I can't install anything. (HowTos)