Gpu problems

[Fikatu]

Hello everyone. Ive bought my pc in january, a prebuilt one. Everything worked like a charm till 2 weeks ago. My pc sometimes crashes, with graphical glitches like green or multicolor squares appearing on the screen and many other glitches but this is the most common symptom. My monitor goes no signal shortly, also my keyboard and mouse lights go off as well and i just have to manually restart my computer. When this first happend i was sure my gpu might be dead. It is an xfx rx 570 8gb. But, what happens to me is really strange. It happens more when i firstly start my pc, and as long as i keep restarting for a few times everythings works perfect, no glitches i can play everything i want for hours maybe without a single crash, good temps good framerates. Sometimes when I stop playing a game and close it, a crash sometimes appears, not everytime. So this is why I am asking you this because my gpu cant be dead, because playing all those games with best quality for long without a single crash is a good proof that my gpu is pretty much alive and working. The problem happens mostly as I told you when i open the PC first time in a day. Besides that, if i put my fans on 40% speed(with msi afterburner) first time when i open my pc I get no crashes or only one, not 3 or 4 till my pc gets usable. I also want to add that when the problem started i put my hdmi on the tv from the computer and i stepped on it and took it out of my gpu slot, ruining the cable, now im using an older one i had in my house, the hdmi cable could be the problem, or maybe the hdmi slot ruined too in my gpu card?

Thank you very much and I hope ill get some responses from you, and ill try to answer quickly if you have more questions for me. Best regards. 

[TylerDurden!]

4 minutes ago, Fikatu said:

i stepped on it and took it out of my gpu slot

get you a new cable  https://www.topdogcables.com/collections/hdmi-cables

[ChaoticChaosx]

Memory test with memtest86 first.

Try a display port cable (if possible) on your monitor as see what happens with that. or new hdmi

[Fikatu]

Ok ill try the memtest then i should try to buy a new hdmi cable this one is a 5 6 years old, the one i stepped on it and  broke was brand new . Thank you very much, ill update you to tell if its fixed, it might help others. 

[Fikatu]

Ok so I tried with new cables. Same problem. When temps are stable it is fine but if it goes too low or too high in a short time it crashes again. If i put the game on pause or smth and it gets from 60 65C to 40C in an instant it crashes. And this is what error i got in just cause 4