Do you have any other Apple software installed, eg iTunes? If so, it may be necessary to uninstall that first, then uninstall Quicktime and any other Apple Software, ie "Apple Software Update".

Apple's Support web site here gives the steps, but I see you have already tried the Add/Remove route. I can't see any quick "Quicktiime Removal Utilities" listed in Google, so it may mean you have to go the manual route.

These are the steps I would try;

I would create a System restore point first.

1] Prevent any Apple tasks from loading at Startup, eg "qttask". Goto Start > Run, type in msconfig and click OK. In the new Window click the Startup tab, and scroll down looking for any Apple or Quicktime tasks, and remove the tick. When you next boot, Windows will give you a message stating you are in "Selective Startup" mode You can suppress that window from within the window itself.

2] Reboot. Close down any Apple/Quicktime icons in the System Tray, (the notification area next to the clock). Return to Add/Remove Programs and see if you can now remove Quicktime and/or any other Apple software.

3] Delete the QuickTime and QuicktimeVR files located in the C:\Windows\system32\ folder. Click Continue if Windows needs confirmation or permission to continue. Then goto the Program files folder, and delete any Apple or Quicktime folders.

4] Using Start > Search, search for any Apple and/or Quicktime folders and files, and delete them. Using the same search window, search for any *.qt or *.qts files, (that is a star, then a period, then qt or qts). The * is a wildcard, and will search for any files with the qt or qts file extension, whatever their file names. Delete those files.

There is a risk here. While I don't know of any other software that uses the qt or qts file extension, there may be other software, (non Apple), that does. The only sure way to check is to open the Properties of each file and check the version information.

5] Reboot.

6] Open the Registry and search for any Apple or Quicktime entries and delete them. Beware, making incorrect changes to the registry can cause serious problems with the operating system, and in some cases cause it to fail completely. Make sure you have a way out, and this Microsoft article may help.

If you would prefer not to do that, use a utility like CCleaner, which will check the registry for errors.

7] Reboot, and re-download Quicktime.

I hope that helps.