Windows update software is taking over my computer.

Based on the information you've given me so far, I don't see any indication that "Windows Update software" has taken over your computer - but one or more updates being offered via Automatic Updates (and which are failing to install) may be playing a role here. [1] 

That being said and assuming it's a Vista 32-bit computer, proceed as follows:

ACTIONS:

[You may want to print these instructions for offline reference.  DON'T SKIP ANY STEP!  If a Step says to reboot, reboot! ]

1a. Right-click on the following link, select SAVE TARGET AS... & download the Norton Removal Tool, saving it to your desktop:  ftp://ftp.symantec.com/public/english_us_canada/removal_tools/Norton_Removal_Tool.exe

1b. Right-click on the following link, select SAVE TARGET AS... & download the McAfee Consumer Products Removal Tool, saving it to your desktop: http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe

2a. Close all open applications (i.e., anything with an icon on the taskbar).

2b. IMPORTANT! => If you have backups of the changes CCleaner Registry Cleaner has EVER made to your computer, restore ALL of them now - then reboot.  See http://www.piriform.com/ccleaner/faq/using/how-do-i-restore-registry-backups

3a. Right-click on the file you saved in Step #1a above and select Run as Administrator. to run the utility. Don't TOUCH your keyboard until the run completes, then reboot.

3b. Right-click on the file you saved in Step #1b above and select Run as Administrator. to run the utility. Don't TOUCH your keyboard until the run completes, then reboot again.

4a. Right-click on the following link & SAVE the download to your desktop: http://iefaq.info/attachments/133/ie8-rereg.zip [2]

Note: Good for IE9 & IE7, too.

4b. Right-click on the file you downloaded in #4a above (i.e., ie8-rereg.zip) and EXTRACT its contents to the desktop. This will create a new folder on your desktop named ie8-rereg.

4c. Close any open applications (i.e., anything with an icon on the taskbar), open the new folder created in #4b above, double-click on the file ie8-rereg.cmd to run the script, and then reboot.

5. Re-assert Internet Explorer as the default Browser in the CUSTOM (<=important!) section of Set Program Access and Computer Defaults. [3]

6a. Right-click on the following link and SAVE the download to your desktop: http://www.slipstick.com/problems/reg/chromehtml.reg [4]

6b. Double-click on the file you saved in #6a above & accept the prompt to MERGE the data with the Registry.

7. Reboot again.

8. Open Internet Explorer (only!) to http://support.microsoft.com/kb/923737 [ignore any DOES NOT APPLY warnings as well as the APPLIES TO section] & run the Fix It.

    Note=> For optimal results, check the Delete personal settings option.

9a. Open Internet Explorer (only!) to http://support.microsoft.com/kb/910336 [ignore the title & Symptoms].

9b. IMPORTANT! => Dismiss/close the automated troubleshooter pop-up! - then...

9c. Ignoring any "Not recommended" or similar warnings, run Fix It 50202 in DEFAULT and then AGGRESSIVE modes. [5]

10a. Reboot once more then test by running a manual check for updates.

  • HOW TO run a manual check for updates
     http://windows.microsoft.com/en-us/windows-vista/How-can-I-tell-if-my-computer-is-up-to-date

10b. IMPORTANT! => Write down the KB number(s) of any updates being offered, and then...

10c. Hide ("Don't show me this update again") all of them (temporarily)!

   • How to Hide or Unhide a Windows Update in Vista
     http://www.vistax64.com/tutorials/72491-windows-update.html

10d. Close the Windows Update applet.

11. Test your computer functionality (including Internet Explorer) for an hour or two.

12. Reply to this post with a status report. In your reply:

    • Include the KB number(s) of the update(s) you hid in #10c above.

    • Also tell me if Avast and/or S*PERAntiSpyware has EVER detected & removed anything (other than third-party cookies).

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[1] cf. http://blogs.technet.com/b/mu/archive/2008/10/02/windows-update-and-automatic-reboots.aspx

[2] Trusted Source: http://iefaq.info/index.php?action=artikel&cat=42&id=133&artlang=en - good for IE9, too!

[3] Only after we've finished this thread, feel free to reassert Chrome as the default if you wish.

[4] Trusted Source: http://www.slipstick.com/problems/this-operation-has-been-cancelled-due-to-restrictions/

[5] Full Disclosure: Running the Fix It in AGGRESSIVE mode will delete your Update History but not the list of Installed Updates.