我想你是有Spyware在你的電腦裡.
以下是我在網上看到的, 來自http://www.cexx.org/problem.htm

One spyware module has been known to spoof a Windows system process so that it cannot be terminated and does not appear on Windows' End Task (Ctrl-Alt-Del) dialogue.

Spyware modules have been implicated in computer problems including system slowdown, Illegal Operation errors, browser crashes, and even the "Blue Screen Of Death".

他所描述的情形跟你所說的很像.
其中他說的Windows System Process就是你說的System.
你可以裝Lavasoft Ad-aware試看看.
http://download.com.com/3120-20-0.h...&search=+Go%21+
兩個都要下載. 第一個是主程式,第二個是更新程式/檔.

good luck!