I need help

so im building my first pc and everything is going great and stuff until when i went to turn it on it wasn’t connecting to my monitor so i looked around and i saw a wire at the very top and it was the cpu power connector that i forgot to plug in but when i plugged it in, my pc wouldnt turn on, but when i unplugged it it turned on but didn’t connect to my monitor can someone help me i have no idea what to do