[ntuner]

I think 4Gb of RAM is also require for ISTA/P.

4GB... Really? :/

Well, that's great!
Then I can start over for the third time, by installing Windows 8 on a laptop I just ran a factory reset on, since ISPI/ISTA can't run(/be installed) on Windows 7 x64!

ISPI next works on both 32/64 bits windows 7/8/8.1/10.
Make sure to install all windows updates before or at least all .net updates

Yeah, it works fine on my Windows 7 laptop, except ISTA/D, since it's missing the SQL files.
And the only way I know hot to get them, is by running the "ISTA_DAT_3.49.10_BIGPACK.exe" file which can't run in 64bit, since it's 16 bit.
(Can't tell you the exact error, since I ran the factory reset)

My Windows 8.1 Pro laptop is fully updated and .NET Framework 4.5 is installed.
I have even tried to download the installer and install it, where it tells me that 4.5 is already part of the operating system, and that the same or newer version is installed.

So I can't do anything more.

EDIT: Even the 4.5.2 offline-installer tells me that the same or a later update already is installed...

As long as you have the right configuration, ista d will install and update the database automatically as soon as you open ista d after the msi is installed. Otherwise you can use 7zip to extract the databases then copy them manually.
You cannot just right click and install the bigpack.exe file since it's not an actual executable file