Blinking power button

I've seen Dell machines blink the power light when there wasn't enough power to actually power them (happened when one of the phases of our building's power blew out). Some machines worked, but notably the Dell's did not. Yours could be an issue of an insufficient and/or failing power supply

Currently, I'm having the same problem with a Gateway DX4640. The customer brought it in stating that the machine said that it found new hardware even though he had not added any peripheral devices to the desktop. I personally broke the warranty seal on the case so I know nothing had been installed internally. When the PC is powered on there is no video signal going to the screen causing it to go in to power save mode. The power light on the tower slowly flashes blue. I've tested the PSU, replaced the PSU, stripped the tower of all components leaving the just the power supply connected and I do get a continuous beeping sound which I would assume is due to lack of memory. During this time there is still no POST. When RAM is put back in it goes back to the same flashing blue light which also happens without RAM except there is then the beeping sound. I've tried swapping RAM, using different memory banks, different PSU, resetting the BIOS, and of course draining the power out of the board. The only thing I have not swapped out is the motherboard and the processor. If someone does figure out how to get the PC out of this sleeping state let us know. If it's not a PC stuck in power save mode then it's probably a bad board.

I had the same prob. with a friends pc. What i did was cleared the cmos. It took a few times for it to clear (approx 6 tries) but then i turned on the pc and it started up. Dont second guess yourself. if the mobo and all other components are getting power then it might not be your psu. every psu that i seen go out did not distribute any power to pc. so trace it back to mobo and start by clearing cmos :)

"I'm not sure if pressing the power button for 30 seconds is the documented way to ""discharge the mobo"" but normally these things have batteries. My experience with an MSI board was to take the battery out, AND short the bios clr (clear) jumper for 10 minutes. Doing it for 5 minutes did not do the trick, it had to be longer for some reason. Note that normally just shorting bios clear will clear the bios, but this board had some manufacturing issues and needed to have the battery removed and the jumper shorted for a while.

Now, if that doesn't help, and I'm betting it won't, unplug everything but the power from the machine, that means the drives and memory too. If you see an onboard piezo buzzer, it should beep at this point when turned on. Plug things in one at a time, starting with the memory (it's okay to put all the memory in at once) and ending with the keyboard. It should beep for a missing keyboard each time.

* 7 years later, someone misread this... UPDATED *
""Unplug everything but the power"" is something you do as you would with any change to your computer's components. You unplug the mains power, wait for the PSU to to discharge (your motherboard may have a light for this), ground yourself, modify the components by unplugging everything attached to the motherboard except the power connector, then proceed to test this and each change in isolation by listening for the POST beeps.
""Plug things in one at a time"" does not mean ""Hot plug things"". Power down after each step, disconnect the mains power, wait for the discharge, ground yourself, add a component back. The step at which your board does not beep, is the step at which you've added a defective component or found a part of the motherboard that doesn't work as intended."