Windows Update has been problematic at times for Win7 (and Vista and 8/8.1) for many months.
This is a solution I found that has worked for me several times and for many others at another forum who had the same issue.
- Download and save, but do not run yet, the standalone installers for KB3020369 and KB3172605 for your architecture (32-bit or 64-bit).
- Disconnect from the internet.
- Disable the Windows Update service in both the applet itself ("never check for updates") AND from services.msc (change it to "MANUAL" and STOP the service, then click "OK").
- Run 3020369 and reboot.
- Run 3172605 and reboot.
- Go into services.msc and change WU back to "Automatic-delayed start" and start the service.
- Reconnect to internet.
- Change WU to "Install Automatically".
- Run a manual check for updates.
If Windows Update is partially or fully enabled when you try this, you will probably get stuck "checking for updates". WU must be disabled first.
If that process does not work and/or you get error messages with a specific error code, then you probably have a different problem.