PING problem,help me!!!

my ping used to be exactly 38(im in canada) when i play crossfire,and these days (for a week)it is sometime 55 sometime 500 sometime 1000,very unstable and i cannot play with such an unstable ping.im not opening emule or msn,and other programms like IE works quite well,the net problem only occurs in crossfire,so it is not network problem i think,and no virus through scan,so what should be the reason?pls help me thx~~~

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