For the past few months I found Win 7 (SP1) updates to be non existent. It would basically be in a never-ending 'searching for updates' phase, with increased CPU activity.
Periodically I would run a so-called fix from MS, or download a KB that purportedly fixed the problem, but did not. Today, I tried the sfc /scannow fix and found a corrupted file, but this didn't help either. My guess is that somewhere down the line, one of the update versions prevented future versions from updating.
So I went hunting for the fix today and tried this, and it worked:
Be sure to check that you have correct platform versions (x86 or x64).
Now I recommend running sfc /scannow from elevated command prompt first anyway. It can't hurt. The linked fix took a little while to take. I ran each patch then rebooted once, then ran update.
Also check that the 'Windows Update' and 'Background Intelligent Transfer Service (BITS)' services are set to run, and/or started.
Then just run the normal update and wait...a wee while...between 1 & 2 hours, and once you have all the new updates, it seems to work a lot faster (minutes).