Went to do something on my computer and it would not come on

[AR69]

Hp all in one pc. Intel core i5-9400T/1TB HDD/128GB won’t come on

[itsmyname]

@AR69 -- any All-In-One computer is quite difficult to do any "part-swapping", to experimentally try to replace a failed component. Basically, "it is what it is".  If you have to ask "how" to disassemble your computer, I think that you should NOT try.

Did you purchase the computer within the last 12 months?  If so, contact HP Support, to open a claim against the HP Warranty.  For any "hardware" issue, HP will repair/replace the computer, at their expense.

Otherwise, take the computer, and its power-supply, to a certified computer technician, and pay for professional trouble-shooting and repair.