Raja,
I'm sorry I didn't respond to this sooner.
I originally had a Corsair GS800 PSU. According to their website, this PSU is compatible with Haswell so I think this angle was covered. I didn't know if there was anything wrong with it though. The PSU was only 1.5 years or so old so I doubt it was going bad. However, I was really itching to get a modular PSU unit. I used this as an excuse so I purchased a Seasonic 650W Modular unit which specifically stated it was Haswell compatible. I removed my Corsair unit and installed the new PSU; the problem did not go away.
I then began to wonder about the memory. I borrowed four sticks of DDR3 memory from work and swapped out my memory with the memory from work. The problem still did not go away.
After 6+ weeks of testing memory, testing PSU, updating all drivers and BIOS, following advice from tech support, waving dead chickens over my system, etc., I came to the conclusion I had a bad motherboard and Asus' tech support didn't argue against it.
Unfortunately, things went bad during the RMA process. Being a professional, I have a need for my system from time to time beyond gaming. I was told the route of sending my board in, letting them fix it, then Asus sending it back could result in at least 3 to 4 weeks downtime which wasn't acceptable.
I went the route of giving Asus my credit information and filling out some paperwork. I was supposed to get a replacement board in the mail, I would swap out my old board with the replacement unit, then I would ship my old board back to Asus.
Alas, after waiting a while (this process was supposed to be completed within 48 hours of receiving my faxed info which Asus tech support did confirm they received during a conversation...), I never got a replacement board. Repeated calls to Asus promised I would get status updates emailed to me and a replacement board would be shipped soon. I never got one. I got to the point I had to give up and ended up canceling the RMA process.
I wasn't a happy camper and decided to purchase a different board to replace mine. I went with a MSI z87-Pro MPower board and have been using it for about two weeks now. So far, my issues have disappeared and am confident they will stay gone.
Looking back at what I went through with the board which I'm not sure I documented here (I had some initial memory usage problems, the USB3 ports didnt' function properly, shut down issue developed about a month after system was running, etc.), I am inclined to believe I simply got a bad board from Asus.
I am concerned though about something. I haven't seen an outpouring of this issue on the Internet. However, I have seen this shutdown/reboot issue mentioned a fair amount and the culprit almost is always an Asus board. Not necessarily Haswell based units but newer ones. Asus may want to check some stuff out here.