Freshly built computer won't turn on after a week
Built my first pc two weeks ago, complete newbie but i did a lot of research beforehand and also double checked every step on reddit and google and the component user manuals and stuff bc I was really paranoid I might mess something up ... took me like 5h to set it all up but when I did it seemed I did a good job - computer posted no problem, I updated the bios, installed windows 10, installed the drivers ... I did forget to plug the four pin argb fan connector to SYS_FAN, so it didn't spin (the leds worked fine tho). One other thing I had troubles with was the network card - I couldn't get it to work properly (bluetooth sound was incredibly janky, it didn't detect any wifi), figured I messed up the driver installation or something ... but I use ethernet and wired headphones anyway so I didn't really pay attention to that lol.
Anyway a week of gaming later (still didn't get over the upgrade from the gaming laptop I used for the last decade tbh, I feel like a caveman entering the spage age 😫) I get home from uni, decide to open it up and connect that fan properly before playing some BG3 on a resolution on which i can actually see the people's faces - I do it, boot it up, everything lights up - ram, ssd, gpu, fan, all fans spin now - but I get no video output. do a LOT of googling but couldn't find anything useful. Unplugged the fans, removed the battery from the motherboard for 10 mins, double checked if everything is plugged in right - the motherboard, the gpu the cpu, (I was sure I didn't touch anything but the fan connector but just in case), even checked with a different monitor just in case, the psu seems to be working fine since the fans spin? So i didn't do the psu test.
I followed a motherboard troubleshooting guide on here that suggested the motherboard might be the issue. From what I know about this stuff (admittedly not much lol) messing with the fans couldn't have damaged my build like this so I'm thinking the computer dying right after was just a coincidence - esp since it seemed to work fine before? Could this be just a faulty motherboard randomly giving out? Did I miss something here that I shouldn't? Really confused rn.
Here's my build (I bought everything new):
PCPartPicker Part List: https://at.pcpartpicker.com/list/ZMXQV4
CPU: AMD Ryzen 5 5600 3.5 GHz 6-Core Processor (€116.90 @ Alza)
Motherboard: Gigabyte B550M GAMING X WIFI6 Micro ATX AM4 Motherboard (€99.90 @ Alza)
Memory: G.Skill Trident Z Neo 16 GB (2 x 8 GB) DDR4-3600 CL16 Memory (€155.90 @ Alza)
Storage: Patriot P400 Lite 1 TB M.2-2280 PCIe 4.0 X4 NVME Solid State Drive (€141.90 @ Alza)
Video Card: Sparkle ORC OC Arc A750 8 GB Video Card (€236.77 @ Proshop - OOS)
Case: Lian Li A3-mATX MicroATX Mini Tower Case (€96.08 @ Proshop)
Power Supply: be quiet! Pure Power 12 650 W 80+ Gold Certified ATX Power Supply (€92.57 @ Proshop)
Case Fan: ARCTIC P12 Pro A-RGB 77 CFM 120 mm Fan (€10.90 @ Alza)