Hello, I recently built my first COMPUTER, I built it all to the manuals, or at least I think I did.
I turned it on for the first time, and it went on for like three seconds, then it turned off. Then it would not turn back in again. I soon realized that I had put in the computer on button and the other front panel connectors in completely wrong, so I rearranged them correctly and the computer still did not work. Did I fry it? Or maybe there is some other problem that I missed in the manual, if anyone could tell me if I fried it or not that would be appreciated.Reversing the front panel header WIRES won't cause damage to the PC...

That being said 3 things to check...all MBoard standoffs in place ? ?...was thermal paste applied properly to the CPU ? ?...and is CPU fan seated fully and proper ? ?what is the make/model of the MOTHERBOARD?
maybe it has LEDs to indicate a fault.
what about the POST (Power On Self Test) beeps, how many do you hear when starting?

did you put the front panel headers on the right pins but the wrong way AROUND, or on completely wrong pins altogether?
like, the power button must have been on the correct pins but you had the HD LED pins shorting out two separate group of pins?