Windows Registry Editor Version 5.00  
右键-打开方式-选择程序,无法使用,说拒绝访问。  
怎么办? 我也碰到过这个问题 刚就出现了  不知道怎么导致的 哎呀 
搜索了一下 这个方法可以解决  
打开记事本 保存为ok.reg运行即可,一般是病毒删除后的关联问题
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