When i want to run the game my windows 8.1 tells me it cant be played, so what do i use to play the game ? as i really really want to play this one as i love its sequal

You need DOSBox. It seems, we even have dedicated thread for that.

I had looked for it but could not find it , thanks for letting me know

But it!
 

The game page should be updated: Instead of "protected/no download" it should say "buy now", because you can buy System Shock 1 (including an Enhanced Edition) e.g. from GOG.com. Or Steam.

I highly recommend doing so.

SS1 is such a classic, everyone should have played it! It is, like UW1, the first truly immersive dungeon crawler... And it accomplishes this by providing a believable setting and backstory. It's not the graphics and it'd definitely not the controls (the mouse focused movement was an odd experiment that didn't last...), but if you overcome those awkward quirks (now a footnote in computer history), you are rewarded with the best first person dungeon crawlers ever to be made. While UW1 is set in the past (kind of), with technology from the middle ages plus magic, SS1 is set in the future with energy weapons (among others), but in a sense the two games are siblings.

If you like the story, but hate the controls... or you like a polished everything (graphics, engine, sound, ... everything except the original story): Go for the remake of System Schock by NightDive Studios. Check out the Demo and www.systemshock.com!

As a sidenote: The source code of System Shock for Mac has been released on GitHub. "Mac" in a context of 1994, when System Shock was released, means something like System 7, which became Mac OS 7.6, compatible till the last classic Mac OS 9.2.2 from 2001. On the GitHub page it says PowerPC is needed, which came as a requirement with the release of Mac OS 8.5 in late 1998. You still need the original game data files to be able to play it though, so buying it is a requirement. With the source code alone you cannot play either, even if you have the data files. And I hear that compiling it yourself isn't that easy...

Sidenote for System Shock 2: In 2013 GOG.com released a fixed version of System Shock 2. Because the game was originally made for Windows 95, it had issues on Windows NT. The released version from GOG includes patches that would finally make it run on Windows XP and up. With additional patches and mods the game is even better on modern Windows PCs. It should be compatible with 64-Bit Windows 10, even though there are optional additional patches, such as a multi-processor patch (the game could crash on systems with more than 1 CPU).