Re: But why does it tell me I only have four days left?
There are two windows for entering numbers. At the very top, but less conspicuous, is the serial number box. In the main dialog window is a more prominantly displayed box for an activation code. If you punch in a serial number here the continue button will remain greyed out. I think the activation code is only used once, when you first buy the product, because I haven't had to re-enter that number yet.
Also, keep in mind PSP X2 is 32 bit software. It may not run on Windows "Home Edition" 64 bit. Only Windows Professional 64 bit and Ultimate 64 bit have 32 bit modes for running 32 bit software.