Windows Update Doesn't Install Updates

I'm having a problem with Windows Update. It's managed to install a few updates, bust most of the updates that it automatically finds fail to install (many important ones too - security updates, etc.). A bit frustrating. For the past couple of days, it tries to install the same two updates every time I turn off the computer. The process takes about 40 minutes. Then it shuts off without an error message. Afterwards, when I turn the computer on again, it doesn't say anything but there are once more two updates that need to be installed - the same ones. It's been quite frustrating. For now, I've got the updates turned off, so it won't try to install them any more, but that's only a workaround and no solution.

I think the problem might be connected with some other installations problems. I've tried to download the updates and install them manually, but it didn't work either; first it said that my virus scanner was interfering (I disconnected from the Internet, deactivated the virus scanner, and tried it again, which got a little bit further but not all the way). At the end I got a kind of dubious error message, which I sadly haven't written down, but it was similar to the ones that I got when I tried to install Microsoft Office and also was unable to get the installation to run through to the end. In both instances, the installation was almost done, after which I got a message that there was a problem with some assembly components, and then it undid the changes. This normally took more than an hour - 30 minutes for the installation to get to the point where it started over, an hour to get it to cancel itself. Haven't found a solution there, and that sucks, because I really need it. I've got a lot of files saved in OneNote format that I can't use and need for work.

The Office error messages led me to a couple of forums where it had worked out because people had updated their .NET framework. I can't do that because .NET is part of the OS framework in Windows 7, apparently. Then I read that some other people had just used Windows Update to update their OS, and then it worked. That's what led me to the discovery that my updates weren't working. I believe that that's got something to do with the problem.I've installed some software, but there's the problem with Windows - I can't install it at all. Not sure what to do here. Windows Update lets me look at the update history. I've found that I get the error code 643 for the two updates that have repeated over the past two days again and again. For the other ones it's a little different; they tried to install once and didn't work. For those, I get following code: 80080005.