My guess is that the game has some compatibility problem with Windows 8, but that's only a guess. Give it meaningful subject line, include the the System Information data you pasted here, identify the game that's giving you problems, and provide as much detail about the problem as you can, including the complete text of the error message, without paraphrasing.

I suggest that you start your own question in the Windows 8.1 Forum -> You'd need to look at making your code more memory/performance friendly. That can be done with the resource module, but it isn't what you're looking for. The most you can do is reduce the limit to a fixed upper cap. Without the specific error messages you get while running the game, it's difficult to guess what might be going on - or how you came to the conclusion that Windows is only allocating 750MB (to what?). It will allocate as much memory as your program needs until your computer is out of memory.

System Information correctly reports your 8 GB of physical RAM, of which 7.89 GB is 'usable' and over 5.5 GB is available at the moment (not being used by whatever is running on your system at the moment). What matters as far as the availability of RAM is concerned is that you have a 64-bit version of Windows.