故障现象：
所有未知格式文件打开的时候，则跳出“该文件拒绝访问”;当点鼠标右键直接选“打开方式”的时候也会弹出“该文件拒绝访问”警告窗口;如果右方已经有部分程序列表，则在点右侧次级菜单中的“选择程序”时跳出“该文件拒绝访问”的警告.
故障诊断：
未知格式文件打开方式关联被恶意修改.
解决方法：
把下面的代码放到记事本中去，改名为*.reg 文件，双击它就会把信息写进注册表，之后就解决问题了!
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Unknown]
"AlwaysShowExt"=""
"QueryClassStore"=""
[HKEY_CLASSES_ROOT\Unknown\shell]
@="openas"
[HKEY_CLASSES_ROOT\Unknown\shell\openas]
[HKEY_CLASSES_ROOT\Unknown\shell\openas\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,25,00,53,\
00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,00,5c,00,73,00,\
79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,73,00,68,00,65,00,6c,00,6c,\
00,33,00,32,00,2e,00,64,00,6c,00,6c,00,2c,00,4f,00,70,00,65,00,6e,00,41,00,\
73,00,5f,00,52,00,75,00,6e,00,44,00,4c,00,4c,00,20,00,25,00,31,00,00,00
*号要用字母代替复制红色区域的内容后，粘贴到记事本中，另存为如 1.Reg然后双击导入注册表即可