Strange Boot Problem

I have a weird problem with my PC right now and I don't know what to do about it. It all started about a month ago, I tried to turn on my PC and nothing happened. Whenever I shutdown my PC, I always turn it off at the plug as I have noticed that even though it is switched off, there are still lights on the back of it that are on which shows it is drawing power. As I am keen to be green, I turn it off at the plug to prevent this happening. So, I was really worried about what might be wrong, and eventually I pulled it out of its plot under my desk to take a look inside. Before I can lift it out thought, I needed to unplug the keyboard, mouse, LAN cable etc which weren't long enough. As soon as I unplugged the LAN cable, the machine sprang to life and booted up! Thinking that perhaps the power cable had been loose (even though I had checked it several times), I carried on as normal. However after shutting it down, the next time I tried to boot I had the same problem. As soon as I unplugged the LAN cable, the machine worked again. As it seemed to be a small thing, I was prepared to just put up with having to unplug the LAN each time I wanted to boot up. But after two times doing this, I became worried that the machine might not turn on at all one day, so although I continued to shut it down, I didn't unplug it from the mains as I had done previously. However, there have still been a few times where I have had to unplug more things to get the machine to turn on (bluetooth dongle, scanner etc). From what I can see, it seems that I have to unplug items that draw power from the machine and don't have their own power supplies but I don't know why this is the case. Last week my area suffered a power cut for four hours and to boot up after that I had to actually open up the PC and unplug my two DVD drives as well as disconnecting my scanner, camera, bluetooth dongle and LAN cable. Once it boots up, I can shut it down and then plug everything back in, but I cannot disconnect it from the mains. Do you know why this is happening, and what I can do to correct it? Normally, I am quite good at fixing problems (thanks to advice from here among other sources) and I actually get lots of requests from friends because of my success in the past but as this appears to be a hardware problem I am at a loss about what to do. Thanks in advance, Joe

My primary concern would relate to your recent area "power cut" of 4 hours.
Yes, it's over now, but it highlights a possible problem that your building's electrical service may be compromised.
And yes, I realize that "the whole neighborhood area" was affected, but your problem has "persisted".
Get a competent Electrician to look at your electrical power access box and the wiring of your house!
________

After the above safety considerations have been attended to:

How many of the "power drawing" devices are "add-ons" that you've installed "after" you purchased the original machine?
Store-bought machines typically have Power Supplies (PSU) that can accommodate the basic hardware and maybe a couple of upgrade hardware additions. However, adding new Hard Drives, Optical Drives, PCI Cards, USB Devices, and peripherals can push the PSU beyond its limit.

If you've added several hardware components, Consider upgrading to a higher Wattage PSU.

Here's a chart-based calculator to estimate your exact PSU requirements for your actual machine:
http://www.zippy.com.tw/P_Budget.asp?lv_rfnbr=2

Best Regards

The power to my area is definitely adequate, that was just an unlucky one-off. But it just served to highlight the problem I had with this machine. I have added a hard drive, a LAN connection, a bluetooth dongle and a scanner to this machine since I bought it last July. So I think maybe it needs a higher wattage PSU as you suggest. Thanks for the help!

One final thing though; how come the machine worked fine for ages and this only became a problem recently? Surely if the power was inadequate, it would have been so from the start? Is it likely there is something wrong with my existing PSU and if there is something wrong with it can it actually harm my machine?

Like any device, PSU's can "wear out". You can get a fairly good look at your PSU output from one or both of the following (free) utilities: Everest 2.20 SpeedFan The actual availability of "read-outs" depends on your machines Basic Input Output system (BIOS) capabilities. Many store-bought machines give poor access to "sensors" which may or may not be built into your system board. Branded machines don't want their customers making adjustments (over-clocking, for instance) so they make it relatively hard for the owner/user to gain access to sensors for Temperature and Voltages. Still you should get some readings and some idea of how well your PSU is delivering what it is supposed to be delivering, by using one or both of the above utilities. When you see the various output catagories 12v 5v 3v and the actual reading of output is significantly different, then you have a problem with your PSU. What's significant……… it depends. Post your results for us to take a look. _________ What if my output results are all as they should be? Well, that doesn't mean that you are not placing excessive demands on your PSU by having new additional Hardware installed. The PSU may be doing everything it is supposed to be doing. And that still might not be enough. Use the PSU calculator link I posted earlier to determine what your presently configured machine may be "demanding". Use Everest and/or SpeedFan to tell you what your PSU is "delivering." Best Regards