Am I going to have to RMA

I just got my pc on a external build. When i turn it on the cpu led flashes once after about 5 sec. of being on then it just shuts down. Ive already reseated the ram and cpu several times and it still does this. If i have to RMA it what parts should it be the cpu, motherboard or RAM? 

Do you have a heatsink on the CPU?

did you check and test psu? could very well be that. if not, please post more detailed specs about your setup, makes it way easier to help. thanks 

h60 watercooler

how do you test the psu?

asus 990fx am3+

fx 8350

gigabyte 7950

1. Open PC case 
2. Unplug power cord 
3. Disconnect all power leads from PSU to computer 
4. Bend a paperclip into a "U" and short the GREEN lead and any BLACK lead on the PSU/motherboard connector 
5. Plug in power cord and turn PSU on. (no it won't shock you)

If the fan on the PSU comes on, then the PSU is not dead. It could be mobo or a short somewhere

 

Just try to reset your BIOS. Clear CMOS