Did you install the WIndows 8 SDK? That's the only thing I know of that contains an SDK specific for 4.5.
Because, if not, I believe you are still confusing "Framework" and "SDK". They are two different things. Most likely you have the 4.5 Framework installed, but PowerBuilder is looking for the 4.0 SDK, and you are trying to install the 4.0 Framework.
You get the 4.0 SDK as part of the Microsoft SDK for Windows 7 and .Net 4.0, which I gave you the link to earlier.