My computer is lagging on games but he shouldn't

[paul.requin]

Hello, so i've been having my Asus PC for about 9 months now, I bought it to play Monster Hunter: World and other games like War Thunder or Skyrim. I could play at at least 45-60 FPS on War Thunder when I got it, with High graphic settings with no problem. My GPU and CPU temperatures were not getting above 70-75°C while playing for a few hours. But now, since maybe 3-4 months, I am getting a lot of frame drops even at low settings, and i now play at around 20-25 FPS on War Thunder. The game starts stuttering after a random time between 5 to 20 minutes. Also, my CPU and GPU seems to heat a lot more, they reach 75-80°C in less than one hour playing. Monster Hunter: World is playable, but the lag and the bad graphics i shouldn't have are really annoying. I keep being under 30 FPS, and I can play only 20 minutes before the game is stuttering. Even though i make pauses and try again later, the game keeps having bad lag.
I tried tests and compared my specs, and i'm above the Recommended specs. Tests from various sites keep telling i should be able to play in 1920x1080 in High settings with more than 50 FPS. But i'm forced to play in 1280x720 with the lowest settings and still lagging.

My specs:

Windows 10 64-bit

Intel Core i7-7700HQ 2.80GHz

NVIDIA GeForce GTX1050 GDDR5 4,0 Go 128-bit
i also have another graphics card: Intel HD Graphics 630

8.0 Go RAM

Possible reasons:

The first one is very important. After doing Alt-Tabs on games, my PC crashed in a strange way. Black screen, and a rectangle with glitched textures in it, a bit like Missingno. After a few more crashes like that (most with Alt-Tabs, but i think one of them occured just while playing.) And i'm quite sure my performances were dropping more and more after those crashes. I did not get another since 2-3 months.
It's also possible that something could have moved inside my portable computer, i know my little brother already hit it. (not strong though, this is probably not a serious hypothesis.) But i don't want to open the PC, it's still under guarantee. Btw, im at around 40°C when launchong my PC, and i easily get to 50° with Discord and Steam.
The overheating seems to be a possibility but i don't know why suddenly my PC would have started overheating.
I installed BitTorrent and uninstalled it... maybe it did something ?

I used the NVIDIA control panel and GeForce experience and set everything to maximum performance and still having lag. I updated my graphics card and tried to update CPU, nothing changed. I made sure my games were using my NVIDIA graphics card and not the shitty Intel thing, i disabled everything that could be running in background, nothing. I also tried to delete all games and cleaning my computer with CCleaner, no changes. I also checked out the battery settings...
Still getting the same kinda lag on WT and MHW after some time.

Help meeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee please !

PS: I probably didn't note everything, can't remember all that happen.

EDIT: Games i play i don't lag on:
League, Brain/out, Besiege, Black Squad, Door Kickers, Risk of Rain, Starbound, Forts...
I DO lag on: Warface, BattleRush, War Thunder, MHW, Evolve and Payday 2.

EDIT: Overheating would seem like the most logic reason, because i do heat more than before and i know graphic cards lower their performance as the heat goes up. Plus 80°C is abnormal after 1h playing. The question is why is it overheating and how can i solve it, if it is indeed the case.

EDIT: I made some tests. My PC can run MHW in 1080p with Low Graphics at 30 FPS with no problem, for like... 10 minutes, starting the game with 45°C for the CPU and GPU. Even after lowering the graphics, my graphics card can't take it, and i'm at around 20FPS. Overheating really seems to be the issue, but, as i said, i can't open it while it's still under guarantee. I would enjoy if you could share solutions to increase FPS and decrease CPU&GPU heating without opening my portable computer.

EDIT: I played MHW this morning and i elevated my PC. I did not encounter lag (i think) but after 25 minutes playing, i quitted the game to check my temp. 80°C. Damn.
This is after 10 minutes cooling. And yes, i'm on a french computer.

 

[paul.requin]

Do you have some ideas ? Cause my average CPU temp is actually freakin' 100°C.

 

[bmockeg]

What is the room temperature?

 

[paul.requin]

Something around 23°C.

 

[bmockeg]

Only option I can offer is a cooling pad, ensure you have air flow under the laptop, use an external keyboard and mouse and prop the laptop up more for airflow underneath.