First, no panic warranted, it is unlikely you actually damaged anything. Second, remove all power from the PSU, do a CMOS reset allowing for some 10s with the jumper in place. Return it to the proper position. Double check the jumper position, use the manual if it isn't clear on the PCB. Try to turn it on.
If it doesn't come up, Turn it off and remove power again. Try to see if your motherboard has any indication of the boot steps. Some motherboards have a double 7-segment display, some have LEDs indicating what is booting up or being checked. Even the onboard speaker (beep sounder) helps. If you are not sure, remove the memory and try to boot, any kind of alarm the motherboard has should fire up. Try to notice any difference in behaviour.
Next steps would be removing SATA devices, GPU, and other peripherals and trying to boot with only the bare minimum. Use a second machine to check if it has booted if you have one (since no GPU will be installed). I'm assuming it's a discrete GPU.