software install/uninstall problems

I hope this is the correct forum for this question:

I have successfully run itunes for some time but I recently tried to install latest version of iTunes. I got a message that Apple Application support was not found and I should uninstall and re-install i-tunes. When I try to uninstall I get message that the system administrator has set policies to prevent this installation. I am the system administrator of my home computer as far as I know. Please make any replies as simple (step by step) as possible as I am not very techy. Thanks

I downloaded the 64 bit version, but right-clicking did not produce an option to run as administrator. I ran it anyway and was told that it could not access the windows installer service. It suggested I might be in Safe Mode (I am not), otherwise contact my support person!

I tried running iTunes from my desktop as Administrator and got an error message:
¨Apple App support not found Error 2. Please uninstall and re-install¨

I then try to uninstall iTunes using the control panel and get the message:
System administrator has set policies to prevent this installation.¨

I then dowwnloaded iTunes from the apple site and iTunes64Setup.exe downloads successfully to my desktop. I try to run this and get the error message that Windows installer service could not be accessed.

I find this last one a little disturbing.

Any suggestions would be welcome
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yes and I get the error message that the windows installer could not be accessed

What is UAC