My computer run 24 hours a day. I turned off the computer for about 3 days and now I can not turn it on. Whenever I turned on the PC (ATX motherboard, celeron 2.6G, 512 MB RAM) it run, everything boots up, lights are on for ONE second and then everything turned off automatically. I found out that when I detached the power cable from Master Hard Drive, the computer can be turned on and everything ( Fan, power supply, CDROm ) ran smoothly. I put the HardDisk to external enclosure and there was no problem reading from it, and the Hard disk boot up normally. What caused this and how can I fix it? Hope you all can help. thank you.

And what does it do when you plug it back in to the orriginal set-up. Does it still shut down after the 1 minute or does it boot up properly? In The Matters Of Style, swim with the current; in matters of principle, Stand Like A Rock "People demand freedom of speech to make up for the freedom of thought which they avoid."

When I plug the hard drive power cable back, there is no response when I turn on the power button. I need to unplug the PC power cable, press the start button couple times to discharged the left over electricity, then plug the power back, and it will be just like before. ONE SECOND booting sound, not one minute, then the entire PC dies again.

If you have power connector that isn't being used, try using it for the hard drive. Or try the power connector from another drive. If that fixes the problem, check the bad connector to make sure none of the pins are bent, broken or spread.

The problem persist. I used power connector from CDROM and spare ones. Some people said that the power supply should be changed to higher wattage / new one. But its just strange that it was working alright and 3 days off should not make the power supply gone bad. any more ideas? Thanks.

Evidently the drive is ok. I would suggest trying another signal cable. While you are swapping it check for bent pins on the motherboard connector. The only other thing that it might be is the motherboard controller. The power supply is possible, but if it was working before, I kinda doubt it.