右键－打开方式－选择程序，拒绝访问，怎么办？

有可能是组策略里面有权限的限制，你修改一下组策略。

运行：gpedit.msc

是注册表被不小心改动了,你按下面的操作做:
新建一记事本,在记事本里写入
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,00,4