Anomalous Computer Issues

[thorhp]

Hey guys, long time viewer but completely new to the forums so forgive me but I'm having these really bizarre issues with my desktop, I'm pretty sure it'd be hardware related since it seems to be multiple things and was having trouble even turning on, not the bootup but literally the power button itself wasn't doing anything while plugged in with the PSU on, but I'll actually get into the issues themselves finally. First thing is really minor but strange, my mouse randomly stops working, specifically the middle mouse button and sometimes wheel, it's spontaneously appears and fixes itself and persists across different mice, it's not an issue with the mouse itself which I initially thought since it's a good but cheap knock off mouse. I also get random inputs from my keyboard sometimes no idea what that is, I'll exit out of R6 Siege and "09" will just type itself into the address of my browser. My computer also restarts itself instead of turning off every first time I shut it down so I have to shut it down twice to actually power off. Also had my computer alert me about being low on memory while playing the Witcher 3 despite task manager saying it was only using 38%, had heavy performance issues, had to restart and then it fixed itself. Another anomaly was when all of the files in my download folder got wiped but not the subfolders and their contents, this has only happened once but it was very annoying. But the most alarming issue was this night when I went to restart my computer to try and see if I could get the mouse issue to go away since it popped up again but when I went to power on it was just non-responsive, of course as I had just been using it the computer was plugged in and the PSU was on but it just did nothing, not a boot issue as not even the lights or fans started spinning up, just nothing, something physical was wrong and just nothing happened, I left the room after trying to figure things out but when I came back it was suddenly booting up mind you I was gone a couple minutes after spamming the power button and trying to trouble shoot the obvious stuff. Some of this I might attribute to malware if not for the other clearly more hardware issues, but I also use windows defender and keep it up to date and it's done the usual scans with nothing wrong. Here's my specs in case that matters. Also keep in mind that this was the first computer I ever built and I did it by myself as an 18th birthday gift a few years ago and I haven't serviced it since then and didn't really do much cable management so I can see something maybe being my fault with something just quietly crapping out or not being done correctly maybe.

MSI Pro Series Intel Z270 DDR4 HDMI USB 3 SLI ATX Motherboard (Z270 SLI PLUS)

Intel Core i7-6700K 8M Skylake Quad-Core 4.0 GHz LGA 1151 91W BX80662I76700K Desktop Processor Intel HD Graphics 530

CORSAIR Vengeance LPX 8GB 288-Pin DDR4 SDRAM DDR4 2400 (PC4 19200) Desktop Memory Model CMK8GX4M1A2400C16 (2 sticks)

G.SKILL RIPJAWS KM780 MX On-the-Fly Macro Mechanical Gaming Keyboard, Cherry MX Brown

EVGA GeForce GTX 970 DirectX 12 04G-P4-3973-KR 4GB 256-Bit GDDR5 PCI Express 3.0 x16 SLI Support Video Card

Cooler Master GM Series G750M - Compact 750W 80 PLUS Bronze Modular PSU (6th Generation Skylake Compatible)

Arctic Silver 5 High-Density Polysynthetic Silver Thermal Compound AS5-3.5G

Cooler Master Hyper 212 EVO - CPU Cooler with 120mm PWM Fan

WD Blue 1TB Desktop Hard Disk Drive - 7200 RPM SATA 6Gb/s 64MB Cache 3.5 Inch - WD10EZEX - OEM

Cooler Master HAF 912 - Mid Tower Computer Case with High Airflow, Supporting up to Six 120mm Fans and USB 3.0

Running Windows 8.1 because I don't trust 10
Also got another HDD that the actual OS is on 'cause I just yanked it from another computer since I didn't wanna pay for an OS
Also an M.2 SSD I use for siege
Sorry if that was a bit verbose for a specs list but I just copy and pasted what the parts were listed as on newegg and amazon

Thanks in advance for any help