Welcome to Vista Forums moxol. I wonder if you are having the same problem as everyone else running Vista: Windows Update spends DAYS checking for updates without finding anything, one instance of svchost.exe consuming tremendous CPU and considerable RAM, cooling fans working overtime, and perhaps you are now months behind on security updates for Vista? In that case, I'm afraid there is no known fix. There is a workaround, thanks to which my Vista PC is fully patched to December 2016; but even that workaround doesn't work as well as it did a few months ago. There is a long-standing forum thread about this issue that started in August 2015 and has grown progressively worse with the passage of time: https://www.vistax64.com/windows-updates/303992-windows-update-just-seems-hang-while-checking.html. If you posted there, you might get a reply containing links such as https://answers.microsoft.com/message/1ef00080-91e9-4ffa-a5a3-92f6ecd69c32. Personally, I'm making a New Years' resolution not to install any more monthly patches that increase headaches more than system security.
Sorry, but I don't know where to find Fix-its that are no longer available from Microsoft.
I had problems with Windows Update, but it worked ok until there were some interrupted updates due to bad connection, and I have to reset it. I did this once couple of months ago, but now I see that Microsoft has removed Fix it. Now I don't know where to find it.
As for Windows Update "Checking updates" problem, only solution is not to click manually Check Updates, but to let it run automatically, it works for me.
Be warned, though. If you are experiencing the same "Checking for updates..." hangs as other Vista SP2 users where Windows Update runs for hours and hours without throwing an error message then MS CheckSUR will likely throw a generic error message (but never actually fix your problem) because the tool simply times out waiting for the Windows Update Agent v7.6.7600.256 (released June 2012) to find available updates. MS CheckSUR might be helpful if Windows Update is throwing one of the errors messages listed at the bottom of the WindowsClub article, but if Windows Update is just running for hours on end you would likely be better off trying the workaround on page 1 of m#l's thread Updates not working, it has been searching for updates for hours in the MS Answers forum that Vistaar mentioned in post # 4.
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