I can’t understand that a computer that was working perfectly fine would just die after one shut down, the power supply is working and it still won’t boot but I’m not getting those flashing Amber 2/1 thing. It just straight up dies after you try to boot. Any other ideas?

2/1 code is "bad motherboard" according to the Dell listing.

For troubleshooting, unplug any hard drive/SSD/CD drive.  Remove the memory and if it has a video card remove it.

Then power on and see what code you get, if it changes or still the same.  If its still the same then 99% its a bad motherboard.

Did you try anything fireberd suggested?  I'd start with the GPU card if you have one - remove it and see if the PC starts.

What GPU and PSU do you have?  If it's the stock PSU, there is the possibility the GPU was too much for the PSU.

I removed everything and it still won’t boot. Me and my friend think it’s a power button issue because when I do the diagnostic button on the back, it gets further than the main power button, still not getting that flashing power button, and also I don’t have a graphics card, any other ideas?

Just so we're not getting mixed up - PC is not going to boot with everything removed.  Point was to see if it would power up and stay on.  Hopefully you put everything back.

Since it wouldn't power up, it's down to either the PSU or MB.  And you got initial 2 & 1 error code indicating it's the MB.

There is another thing to try - While keeping the test button in the back pressed first, push the power button in the front and see what it does.  I had another user do that.  PSU seemed to be on it's way out, but would still fully power up with the test button pressed.