Poor performance in gaming. Too much ambiguity! Please help!

Here's the problem. I'm running windows 10 build no. 14352. I know it is expired now and my PC restarts every few hours.
The thing is like this, im experiencing poor performance in gaming.
My laptop has 8gb ram, i5-5200u, nvdia gt-940m.

the date was 13 July. I was gaming normally, decent fps with ac black flag @ 1280*720 about 30-40 fps medium-high settings and about 30fps @custom ultra (1366*768) in rainbow six siege
two weeks ago i started receiving messages that this build of windows 10 will expire on 15 July The internet connection was a no-go so i couldn't download the latest build which now is 14390.

on 14th or so, when i was playing, there was a bad performance. 20 something fps in ac black flag even at 800*600 and unplayable fps in rainbow six siege.

Now (as of 17th July), even the "big picture" mode of steam operates poorly, although windows animations and transitions are smooth. The Nvidia GPU monitor shows that the game is using the GPU but the game runs as if the integrated GPU is used. Any game for that matter.

Is this like windows 10 crapping on me just because it is now expired or what?

I tried disabling Intel GPU, no avail... performance poorer than before.

What is the solution? will updating to latest build of windows will solve the issue?
Is this a graphics card issue? But it doesn't seem so because its so sudden and also after 14 July.

You'd probably be better off doing clean install and all the drivers. Drivers are usually most to blame for poor performance. You can also try with update and see if that fixes some things, expired windows start deteriorating with time and there were many updates that do address some problems from earlier versions.
You may be best off waiting until August 2nd when newest full version is supposed to be released.

Check settings for your primary GPU driver or even turn off IGPU in BIOS if you can.