Sometime updates get corrupted, which can cause a continuous download loop in some applications. I also had a recent situation which appears to affect a particular version of Windows 7 x64, though I do have a patch installed. OS updates would not completely download, and would freeze the update install process due to what appears to be corrupted files. I suspect that the issue was caused by a particular API that is commonly used to filter web traffic.
The fix was to close or uninstall the application when downloading updates. But also had to clear out the previous downloaded updates and indexes, and let Windows rebuild it to allow it to re-download the previously corrupted files.
The question may be what caused the downloaded files to be corrupted in the first place? Which assuming its not on the network side, can potentially include any application that filters web traffic data, such as firewalls, AV software, network monitoring apps, etc.