After you unplugged it, did you plug it back in and turn it on? If so, what happened at that point?

As far as unplugging and plugging USB devices, in some cases, you need to stop them in order to safely remove them. There's an icon with a little grean arrow above it that says "Safely Remove Hardware" when you hover over it. That lists the devices that need to be stopped to remove them safely.

So what do you get when you turn on the power, just a black screen?

There's no telling what occured, we could guess the power supply, motherboard, or the Windows Registry has been corrupted, sometimes a surge can occur buy unplugging things with the power on, more often then you end up with an error like this:

C:\windows\system32\system missing or corrupt.

If the computer will not boot to the welcome screen or safe mode, you will either do a recovery using recovery discs, or a Repair install using a retail version of windows xp. put the xp cd in boot and do a repair..

When you power up, what error do you get if any, or maybe you get a black screen with a cursor blinking?

I did plug it back in. The APC red overload light was on, so I turned it off, unplugged everything from it and plugged all of the cords into a surge protector strip and turned it on. The yellow light was still on, fan was on, but no response from anything I did. The screen was black. As for the USB cords, I have 4 2.0 USB connections on the back of the computer.No Disconnect Hardware option for those. They are for printers, scanners, extra drives, etc; The scanner setup actually says it is OK to connect it with the power on.I have 4 on the front for memory cards. Ida

All usb ports can be hot swapped.. without error.

Some hardware does not support this. and will need to be stopped. Using the icon in the task bar. Or in system settings. I would try unpluggin all usb devices.

use the ones that were not used by your printer, for you mouse and keyboard if needed

and see if you can boot up..

Sometime when u do this and it does not support hot swapping.. u can fry your usb ports/motherboard. or the device your trying to unplug/replug.

It's rare that a pc will be rendered useless from this unless u caused physical damages to the ports.. and connections are shorting..

Hope this helps. let me know if it turns on.. a solid or blinking light. usually means there is a connection short somewhere.. If you jolted your system.. you'll need to check all connections.. inside and out.. for proper fiting. or damages.. includeing that usb port..

Here is a link that might be useful: My website

I would remove all unnecessary items from the equation, plug the pc directly into the wall, eliminate the strips and power supply for now, But before you plug the pc into the wall, with pc turned off and unplugged, disconnect everything from the pc that has power going to it, like printer, router, etc. Then on the back of the pc there is a toggle switch that turns off the power supply, switch that to off, let it sit for 10 mins or so like that. Then in this order try again, plug in your items that were plugged into the pc, plug the pc into the wall outlet, turn the toggle switch on the back back to on, Push the power button on the front of the tower to power up the pc. See if that makes any difference, many times if it was a power issue disconnecting everything and letting it set a bit will reset it.

the safely disconnect icon they are talking about is not on the back of the pc near the usb port it is on your monitor screen just below the clock in the systray, when you put your mouse over it it will show what is plugged into usb ports, you select the item you want to disconnect and wait till it tells you it is safe to disconnect, that should be done for everything plugged into any usb port anywhere on the pc, everything that gets plugged in will show up in the list.
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I like Ravencajn's ideas. If you try her approach and you still have no luck, I'd take it to the next level. After unplugging everything and letting it sit, leave everything except the monitor, keyboard and mouse unplugged when you plug it back in. Then turn it on and see if it boots up. If it does, plug in things like speakers, network cables etc. Do them one at a time and make sure the computer is working before going to the next item.

Once you get to that point, start with USB devices. Again, do them one at a time and make sure they're working before going to the next one. If you're using USB hubs, unplug everything that's plugged into them, plug in just the hub, make sure it's all working, then plug the devices into it, one at a time (again making sure it works after each one).

I also have another question for you. When you say the yellow light is on, what is the yellow light? The power? The drive activity light? something else?

I don't like the APC overload light going on. Did you reset the APC? Is this a UPS or one of their surge suppressors? Does the manual for it say it can be reset and used once that light goes on, or are you supposed to replace it? I had a UPS go out when the power company did some work outside. The computer, printer, etc were all undamaged, but I had to get a new UPS. If I hadn't had the UPS, I'm reasonably certain I'd have lost the PC and the printer.

I suspect the lower voltages on the power supply have burned out. The fans run indicating 12 volts but nothing else. Besides the orange light Ida is the activity light blinking or showing at all? The red light on the APC is also a sign the power supply has failed.

Do this before trying to restart your computer, you do not want to fry the motherboard. Remove the left side of the computer and read the make and model of the power supply for us. Do you see burn or black smoke marks? Did you smell any kind of burning? Leave the side off if all looks good so that when you try restating you can watch inside for wisps of smoke rising off the motherboard.

Give us a make, model and age of the computer please.

Well, once again, I am deeply grateful to all of you. I always get help when I come here and sometimes I don't stress THANK YOU enough. I got up this morning and found all the posts and hardly knew where to start. Everything was already powered down, so I started unplugging everything from the power supplies and then all the usb connections except the printer. Flipped the swith and all looked the same as yesterday and then the yellow "drive" light started blinking so I knew it was alive. It loaded right up and all seems normal except I'm running in bare bones mode. No printer, no nothing. I'm going leave it that way until Monday when the computer guy gets here, as I am afraid I have a power problem. The guy that is coming built this computer in his shop about 4 years ago and he knows my system inside and out. Right now, I am just so happy that I still have a computer and all my stuff seems to be intact.
Thanks again! Ida

Oh, good news Ida. It has started and running Windows so perhaps no major hardware damage. If your computer was locally built then he would have installed an adequate power supply no doubt. My fear was that this might be an eMachine because they had real problems with power supplies failing.

Please let us know what your techie fixes so we can all be slightly wiser.

I have to admit I thought you were dead in the water...

Glad it booted up...

Me too zep! I wouldn't have bet a nickel on it. I even had a new laptop in the shopping cart! Then after I got everything all loaded back up and running on this one, I thought, well, I do need a backup, so went ahead and ordered a new Gateway while they can still be had. I was using my son's laptop to post last night. But you know, I would rather have this old friend than a brand new one! You guys and gals do a great job at helping all us computer challanged grannies. Ida

excellent news idaf! I have seen several come back from what I thought was sure death by doing the full electrical cycling by unplugging every single thing and turning off the switch on the back then letting it set that way for a while.

Glad that seems to have got you going again maybe you just will need a new usb port and that is very easy to replace.
Do keep us updated on what happens!