I bought a new monitor plugged it all in (DP) and the monitor says "No DP Cable" the monitor works with HDMI but I can't set it to DP and not sure why. I tried looking up reasons why it wouldn't work online and kept finding "cable isn't pushed in far enough" mine is for sure all the way in.

If anyone could help me on this I'd appreciate it thanks

defective cable or card or monitor even.

is there a way to know what's defective? I should mention when I tried plugging my hdmi cable in the hdmi port on my computer next to where the DP ports are it didn't work either I had to plug it into a different one

swapping out the hardware with known working parts.
IE trying said cable on a working card or monitor.
Logically this rules out hardware then you can worry about settings/software.
But I'll assume your monitor is set to dp if it doesn't auto recognize the input.
I don't know if a dp port can be disabled on a gpu tbh though I see zero use in that.
and cables can break or be defective at anytime.