I take it the PC is dead now so we can't have it tell us more. Let's hear the make, model of the PSU and other parts.
If you can boot it, add the PSU detail and a Web Speccy. Read https://www.piriform.com/docs/speccy/using-speccy/publishing-a-speccy-profile-to-the-web
This may be long, but I need help. First, my graphics card because it all comes from it, I think: old GTX 660ti 2gb and now GTX 1060 6gb.
Long story short, after 4 years of good use, my 660 ti overheated and basically stopped working (in the last month, it was at a constant 75-80 C when in-game), so I bought a GTX 1060 6gb from Gigabyte. After about 2-3 hours of tweaking in my PC with the PCI cable and the Bios, it finally ''worked''. I say that because, my PC detected the GPU, but according to GPU Tweak, the clock boost was at 606 instead of 1771 and the memory clock was at 808 instead of 8008. I had to manually set everything everytime I started my PC, because it couldn't save the settings, despite my research and attempts. First 2 days, everything fine, excepts the GPU Tweak thing. Third day, I start my PC and the desktop and everything is running at about 0.1 FPS, I am not joking, I cannot do anything. I decide to restart my PC and everything is fine. Fourth day, being today, I start my PC and the first 2 hours or so are fine, until it starts to lag like yesterday, I restart it, all good for about 15 minutes, then lag and now as soon as I get on my desktop, everything drops to that 0.1 FPS. Last time I tried (about 20 minutes ago) the screen went black, then back on, then all sorts of colors appeared, then black, then colors and I decided to shut it down. So here I am on my laptop with no clue as to what to do. Just so you know, everything was fine with my old GPU, I haven't downloaded any program or gone to any weird websites in the last 4 days.