There are many reason why Windows Update fails. Here is the best solution to solve the “Windows Update not working” error. Please follow these detailed steps below, and then your windows update will work again.

Firstly, double click the time at the end of your taskbar. Make sure your computer’s date and time is set correctly. Wrong date and time often brings the “windows update not working” issue.

Secondly, have a look at your firewall software. If your firewall blocked Microsoft.com, you can’t update your windows correctly.

Thirdly, are you using a Proxy server? Open your Internet Explorer, then click “Tools” menu, click “Internet Options”, click “Connections”, click “LAN Settings”. If you are using a proxy server, uncheck “Use a proxy server” and have a try. Please NOTE: If it doesn’t work, please restore the proxy server settings.

Fourthly, download this tool(click here to download), and have a free scan. It has a One-Click Maintenance to repair computer errors. After that, your PC will work at a perfect health.

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Windows Update Hexadecimal Error Number and Descriptions(for advanced users): 
0x800C0002, 0x800401E4 and 0x80072EE5  The address of this site is not valid. Check the address and try again. 
0x800C0003 Cannot start an Internet session. 
0x800C0004 and 0x80072EFD  Cannot connect to the Internet server. 
0x800C0005 Cannot locate the Internet server or proxy server. 
0x800C0006 and 0x80072EFC  The site reports that the item you requested could not be found. (HTTP/1.0 404) 
0x800C0007 The Internet site reports that a connection was established but the data is not available. 
0x800C0008 Cannot download the information you requested. (This is an incorrect date on your PC or a server certificate revocation!)
0x800C0009 The item you requested requires proper authentication. (HTTP/1.0 401) 
0x800C000A The Internet site cannot return the object you requested. (HTTP/1.0 403) 
0x800C000B and 0x80072EE2  The connection to this Internet site took longer than the allotted time. 
0x800C000C The site reports that the request is not valid. 
0x800C000D and 0x80072EE8  The required Internet protocol is not installed on your computer, or the Internet address you requested may not be valid. 
0x800C000E A security problem has occurred. 
0x800C000F and 0x800401EA  Cannot open the specified file. 
0x800C0010 Cannot start the program needed to open this file. 
0x800401E6 and 0x80040154  No program is registered to open this file. 
0x80004004 The hyperlink cannot be followed to the destination. 
0x801901F8 The transfer request timed out while waiting for a gateway. Resume the job at a later time. (HTTP Error 504)
0x801901F7 The service is temporarily overloaded and cannot process the request. Resume the job at a later time. (HTTP Error 503)
0x80190190 Proxy Error: Host name not recognized or host not found (HTTP Error 400) Download this patch, install, reboot and try again. Q823718 
Reference:http://support.microsoft.com/kb/555989