System keep rebooting

[Christianm]

Hi everyone, 
my four year old PC has started to create problems for me now. for last one week when i was starting a PC, motherboard was showing the q-code 9A and vga_led remains ON for around one minute or sometimes less and then system starts.
today when i start my PC it worked fine for few minutes and then windows started to shut down itself and system just keep rebooting in 2-5 seconds. no display no nothing. there was no warning, no blue screen, nothing. 

so far I tried:
clear CMOS
reseated the battery
remove all devices (graphics card, sound card, HD, mouse, keyboard, chassis power & USB cables, fan cables)
I have four DIMMs, tried all one by one in all four slots

when i turn my PC on after 10 minutes or so, it starts but after 40-50 seconds it reboots like i mention.

so does anybody have any clue what is the problem? is it PSU or motherboard or something else.

My PC specs:
core I5 4440
asus maximus vi hero with BIOS updated to last released (long ago)
16 gb ram
asus gtx strix 750Ti 2gb oc
sound blaster z
corsair hydro H45

[MrDrWho13]

What's your power supply?

[Christianm]

cooler master gx 550w 80 plus

 

http://www.coolermaster.com/powersupply/gx-series/gx-550w/