Since your unsure whether you updated your bios correctly you should eliminate that as a problem. go here and get the latest update ASUSTeK Computer Inc.
the download should have a tool which will format a usb or floppy for you to boot from when you load up your computer. But it may be easier if you just download the windows flash tool which is in that download index aswel. this way you can just use the tool to select the bios downloaded file and it will flash in windows.
The best way to test your psu is get a friends or a spare and see if problem persists or grab a cheap psu tester which has LEDs to tell you if it is working correctly. It may also prove to remove all ram except the module closest to the cpu because it sounds like a ram problem, trying booting which a couple of different stick since one could be bad.