Only the fan turns on but no power

Anant Singh, sounds to me like you are having power supply problems. The reason why your fan comes on is probably due to the fact that your 12V is still working, but your probably lost the rest. Check all the connections with a multimeter and check the switch first, make sure it works properly, after that check the voltage on the power supply. Checking the wiring will be a little tougher since you modded your Xbox. Check the PSU for blown Caps and fuses. Good Luck.

Maybe it's the 5volt pin problem, also I have a problem that my Xbox keeps giving me the 3 flashing rings, it is not overheated, is it because the atx power supply I use is just cheap? Also whenever I stop the atx power supply fan, and keep it running, it works fine, so what is it, also could a 12 volt and 5volt 2amp power brick work, I tried it but it gives me the red flashing rings, pls help

So was the consensus that the old ATX PSU died? I've done the same thing with an Xbox one, worked fine for about a week or two and now I just get nothing at all unless I manually turn on the PSU with by shorting the PS_ON line to ground, when I do that though I get full fan and no ability to turn the Xbox on, it just makes an attempt at the on sound but doesn't actually do anything from there. All my voltages are reading correctly, but I can't seem to measure amperage in any capacity. I guess I'll jury rig another PSU to see if it's the issue. Was a cheap one from the road side anyway.