4 pin 12v atx problem

So i came home today only to find out that the pc shuts down immediantly after eatch boot.aftee cleaning and researching,turns out the 4pin cable from the psu is the reason.when it isnt connected the pc runs like it should.and when its connected it shuts down right away.i tried cleaning etc. But it wont help.ideas?
Specs on my profile.writig this on my android.sorry for my lazines

Strange. If it is indeed the 12V ATX connector (2 yellow and 2 black wires), then your system shouldn't power on at all if it is removed since this provides the electrical supply to the voltage regulator(s) which supply the processor itself with the correct amount of power.

If it is an auxiliary connector for a peripheral such as a FDD or HDD, then that would make sense if the peripheral is faulty.

Disconnect all peripherals and case fans (DO NOT disconnect the processor fan) and reboot. Don't worry about not being able to find an OS, as this is normal until you have reconnected the HDD. If it now boots (and hangs on the OS not found screen), try adding the peripherals back one at a time and recheck. Don't forget to power off when connecting/disconnecting any of the power leads.

Sorry it took so long to anwser.

Iv done so already in the past and it still doesnt work.im going to get a second PSU later today and perhaps fix it(if its the psu).any other ideas?

It could well be a faulty PSU. Although I said that a system won't power on without this connector, it isn't always strictly true. It can, in some cases, power on without this connector, however this causes stress on the motherboard wiring (the tracks carrying 12V can literally burn out).

Good luck with the replacement PSU. Make sure that it is a reputable make, and with sufficient capacity for your system.