I think something ghastly may have happened to the Access Control Lists (ACLs) on your system, Lebz. There's just too many permissions errors cropping up for this to be a happenstance thing.
Usually, when people suffer from something like this, we try using a batch file for the subinacl tool. Unfortunately, the relavant script we use is designed for 32-bit systems:
[Solving setup errors by using the SubInACL tool to repair file and registry permissions|http://blogs.msdn.com/astebner/archive/2006/09/04/solving-setup-err ors-by-using-the-subinacl-tool-to-repair-file-and-registry-permissions.aspx]
In addition to the advice given by Mr Stebner in the
Comments to that blog entry:
Hi Dharamg - The reset.cmd script currently doesn't work on 64-bit operating systems. I can post a fix later, but in the meantime, all you need to do is change the item that says %ProgramFiles% to say %ProgramFiles(x86)% instead and then it should run correctly. The error you see about "subinacl is not recognized..." means that the full path listed for subinacl.exe in reset.cmd doesn't match the location that it is actually installed on your system.
... I think it's plausible that you might need to add another line granting permissions to the Program Files (x86) folder too. But I'm not sure about that.
So, perhaps it might be best to post a query at the blog there, asking if you need to do that or not.