求教: 我的電腦不允許裝軟件?

每次我想安裝新軟件, 如Visio, Simply Account, SPSS 等, 我的Win 2000 Professional 總顯示:

C:\WINNT\SYSTEM32\AUTOEXE.NT, The system file is not suitable for running MS-DOS and Microsoft Windows applications, Choose"Close" to terminate the application.

但是我以前是能裝的, 真是急死我了, 求各位大俠幫忙.