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根据您的描述，应该是您的电脑中和更新有关的注册表丢失导致的问题。
我们可以试试手动为您添加这个服务，如果添加后还是无法解决这个问题的话，那可能您的问题涉及更多的故障，由于您也不清楚之前发生了什么，所以我们也无法为您进行还原，要解决这个问题依然需要您重新安装系统来解决。
1，重建注册表
打开记事本，将下列内容复制进去
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\wuauserv]
"PreshutdownTimeout"=dword:036ee800
"DisplayName"="@%systemroot%\\system32\\wuaueng.dll,-105"
"ImagePath"=hex(2):25,00,73,00,79,00,73,00,74,00,65,00,6d,00,72,00,6f,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,\
00,76,00,63,00,68,00,6f,00,73,00,74,00,2e,00,65,00,78,00,65,00,20,00,2d,00,\
6b,00,20,00,6e,00,65,00,74,00,73,00,76,00,63,00,73,00,00,00
"Description"="@%systemroot%\\system32\\wuaueng.dll,-106"
"ObjectName"="LocalSystem"
"ErrorControl"=dword:00000001
"Start"=dword:00000002
"DelayedAutoStart"=dword:00000001
"Type"=dword:00000020
"DependOnService"=hex(7):72,00,70,00,63,00,73,00,73,00,00,00,00,00
"ServiceSidType"=dword:00000001
"RequiredPrivileges"=hex(7):53,00,65,00,41,00,75,00,64,00,69,00,74,00,50,00,72,\
00,69,00,76,00,69,00,6c,00,65,00,67,00,65,00,00,00,53,00,65,00,43,00,72,00,\
65,00,61,00,74,00,65,00,47,00,6c,00,6f,00,62,00,61,00,6c,00,50,00,72,00,69,\
00,76,00,69,00,6c,00,65,00,67,00,65,00,00,00,53,00,65,00,43,00,72,00,65,00,\
61,00,74,00,65,00,50,00,61,00,67,00,65,00,46,00,69,00,6c,00,65,00,50,00,72,\
00,69,00,76,00,69,00,6c,00,65,00,67,00,65,00,00,00,53,00,65,00,54,00,63,00,\
62,00,50,00,72,00,69,00,76,00,69,00,6c,00,65,00,67,00,65,00,00,00,53,00,65,\
00,41,00,73,00,73,00,69,00,67,00,6e,00,50,00,72,00,69,00,6d,00,61,00,72,00,\
79,00,54,00,6f,00,6b,00,65,00,6e,00,50,00,72,00,69,00,76,00,69,00,6c,00,65,\
00,67,00,65,00,00,00,53,00,65,00,49,00,6d,00,70,00,65,00,72,00,73,00,6f,00,\
6e,00,61,00,74,00,65,00,50,00,72,00,69,00,76,00,69,00,6c,00,65,00,67,00,65,\
00,00,00,53,00,65,00,49,00,6e,00,63,00,72,00,65,00,61,00,73,00,65,00,51,00,\
75,00,6f,00,74,00,61,00,50,00,72,00,69,00,76,00,69,00,6c,00,65,00,67,00,65,\
00,00,00,53,00,65,00,53,00,68,00,75,00,74,00,64,00,6f,00,77,00,6e,00,50,00,\
72,00,69,00,76,00,69,00,6c,00,65,00,67,00,65,00,00,00,00,00
"FailureActions"=hex:80,51,01,00,00,00,00,00,00,00,00,00,03,00,00,00,14,00,00,\
00,01,00,00,00,60,ea,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\wuauserv\Parameters]
"ServiceDll"=hex(2):25,00,73,00,79,00,73,00,74,00,65,00,6d,00,72,00,6f,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,\
77,00,75,00,61,00,75,00,65,00,6e,00,67,00,2e,00,64,00,6c,00,6c,00,00,00
"ServiceMain"="WUServiceMain"
"ServiceDllUnloadOnStop"=dword:00000001
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\wuauserv\Security]
"Security"=hex:01,00,14,80,78,00,00,00,84,00,00,00,14,00,00,00,30,00,00,00,02,\
00,1c,00,01,00,00,00,02,80,14,00,ff,00,0f,00,01,01,00,00,00,00,00,01,00,00,\
00,00,02,00,48,00,03,00,00,00,00,00,14,00,9d,00,02,00,01,01,00,00,00,00,00,\
05,0b,00,00,00,00,00,18,00,ff,01,0f,00,01,02,00,00,00,00,00,05,20,00,00,00,\
20,02,00,00,00,00,14,00,ff,01,0f,00,01,01,00,00,00,00,00,05,12,00,00,00,01,\
01,00,00,00,00,00,05,12,00,00,00,01,01,00,00,00,00,00,05,12,00,00,00
2.将文件另存为wuauserv.reg
3.执行您保存的reg文件，导入注册表。
4.搜索CMD，以管理员模式执行
5.输入下列命令
sc create wuauserv binpath= "C:\WINDOWS\system32\svchost.exe -k netsvcs" type= share start= auto displayname= "Windows Update" depend= RpcS
6.重启电脑后打开服务，查看服务是否可以被看到并执行。
免责声明：修改注册表或工作组通常是面向高级用户、管理员和IT专业人员，它可以帮助修复一些问题，但是，注册表修改不当可能会出现严重问题。 因此，请一定严格按照下列步骤操作。 为了获得进一步的保护，请在修改注册表之前对其进行备份。 有关如何备份和还原注册表的更多信息参考：如何在 Windows 中备份和还原注册表
如果以上操作完成后，出现了报错信息，请告诉我们，我们将根据您提供的信息修正提供的方案。
希望以上信息能够帮助到您。 如果我的理解有误也麻烦您能指出，以便于我能更好的协助您。
Lugoo Bei|微软社区支持专员