Losing FPS

Ive had this problem for a while now and I just want this fixed... so the problem is that my computer is working more then fine a few weeks getting nice FPS no lags no nothing but then suddenly my computer starts to get really bad FPS starts to lag and **** like that, have someone had this problem or know a solution to it, please let me know. :)

SPECS
i9 9900k
RTX 3060
ROG STRIX Z390-F GAMING
PSU EVGA 650w
16gb RAM
2 ssd's one with 500gb and the other one is 1tb.
 
Low FPS in a certain game? One cause is incorrect graphics settings like turning on Vsync but your rig can not deliver that frame rate in certain areas of the game so it slows down (lags). I use the Geforce Experience all the time to handle my settings and I have never regretted it.

Maybe you could check the Event Viewer which logs errors with time stamps. Check the logs at the time you experience the lag. Maybe there is a related problem of service that is causing the lag?

Just a couple ideas to get you started.
 
It is in the most games expect CSGO for some weird *** reason my fps is good there but in Fortnite Overwatch the FPS is sooo damn low for my specs that I have, on Overwatch I can get down to 180 sometimes even 160 FPS at lowest settings, but when the computer is working correctly I get about 250 FPS with kind of good settings. In Fortnite when the computer is working fine I get 300+ FPS with everything low and performance diectx thingy, but now I barely get 250 when I am in fights. What should I look after in Event Viewer? I usually have everything on low and not V-Sync enabled in Fortnite, but in Overwatch I use V-Sync sometimes because my game is running much smoother (usually when my computer is working fine). I actually tried to put on Geforce Experience but my FPS got worse.
 
Geforce Exp. would make frame rates worse if you are going for high FPS eith low detail settings, on that I agree. I use Geforce Exp. for settings that make the game look pretty. Vsync will have to stay 'off' and you have no choice but to live with the tearing on the screen until you can got a Freesync or G Sync monitor.

Losing 50fps in heavy on-screen action is not unusual and the old game engine that Counterstrike uses is renowned to yield lots of FPS even on modest hardware. Your card is one of the latest video cards and it will fare best at 1920 x 1080. Its when you use 2560 x 1440 (or higher) and higher detail settings that the 3060 will have some trouble.

Event Viewer shows red errors...check 'em out and Google search the errors that stand out to you with matching timestamps to your in game slow downs.
 
Click 'Custom Views' click 'Administrative Events'...take a look through there. Be aware that red & yellow alerts here are a normal part of the operation of a computer but some of these may indicate a problem that needs attention. I realize it takes a trained eye to spot the trouble but you have to start somewhere.
 
Some other possibilities:
The machine is heat throttling.
The machine is infected.
There is too much crap running in the background.
You voluntarily have too much crap running while you try to game.
 
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