Power consumption from your USB hub, or your mother board. I suggest getting a better hub or larger power supply/it could also be your motherboard's usb connectors not drawing enough power (****ty motherboard).

Would that apply if the HD draws it's power from an AC outlet?

Which HD are you referring to? The external?

New external HD, with AC connection. I've tried both a simple wired mouse and a wireless mouse.

What can I do to correct the problem? I'm trying to get my files, pics, etc. off this PC so I can install them on another one. My motherboard is MSI 865 PE Chipset... Will it do any good to take it to a pro, just to copy my C drive?

From what I get from this you are trying to wipe your C drive and reinstall a new OS? FYI you can't just copy and paste all your games, and software and expect them to work after. Not saying your doing that. Maybe you have a new mouse and you haven't install the driver? Maybe your USB 2.0 has gone haywire? What operating system are you running? If your running win7 forget about the usb going haywire. Have you tried plugging your mouse into different usb ports? Each port runs independently through your computer. If you have XP try downloading this driver, if you already have it try it anyway. http://www.softwarepatch.com/utilities/via-usb2.html *Don't click the ad that says start download.*

From what i get from this you are trying to wipe your C drive and reinstall a new OS? FYI you can't just copy and paste all your games, and software and expect them to work after. Not saying your doing that. Maybe you have a new mouse and you haven't install the driver? Maybe your USB 2.0 has gone haywire? What operating system are you running? if your running win7 forget about the usb going haywire. Have you tried plugging your mouse into different usb ports? Each port runs independently through your computer. If you have XP try downloading this driver, if you already have it try it anyways. VIA USB 2.0 Driver 2.7 download for Windows (http://www.softwarepatch.com/utilities/via-usb2.html) *Don't click the ad that says start download.*

The OP said nothing about wiping her drives. She is simply pluggin an external HDD in to copy files too it and this causes the mouse (wired or wireless) to stop working.

No, I want to back up all my pics & docs. If you know of a place to download just a usb driver, I'll try it. I'm not going to pay $30 and take a chance of this site messing with all my drivers. I've been sucked into that con before.

If you go into device manger are there any yellow shields next to USB ports?

Right-Click MY COMPUTER
Click MANAGE
In the left pane CLICK DEVICE MANAGER
Look for Universal Serial Bus Controllers

Do you use a wireless mouse?there could be something wrong with the route that your hard driver may affect your mouse.since I just got a new optical mouse (http://www.dealstudio.com/searchdeals.php?type=id&q=d208929&ru=286073),do the excellent work,so you can just have a look.

No, there are no shields in my device manager, and no conflicted hardware reported.

I have tried both wired & wireless optical mouses. Both quit working when I turn on the HD.