What model PC and Operating System? 

That is needed for someone to give you specific assistance.  There are many Dell Models and configurations.

I have a Dell 8250 Dimension and I run Windows XP. Thanks

I do have the latest updates from Microsoft. I will say this. My computer came with an internal floppy disk drive and when it quit working, I took it to the computer repair shop. They told me something had gone out in the motherboard. I asked if I could use an external floppy disk drive and they said yes, but I wonder if this has anything to do with the external one not working. Any suggestions.

If you are trying to connect it to the front of the PC, try one of the rear USB jacks and see if that works.  On some model Dell's there is more "power" available on the rear connectors and the USB drive is the type that gets it's operating power from the PC may need more power than is available at the USB port(s).

Another possibility is to us a Powered USB hub (one that has it's own power supply) as there will be more power available with the powered hub.

Do you have the latest Windows XP updates, including SP2?  If not, download and install the updates and see if it makes a difference.

The USB is separate from the IDE channels on the motherboard.  I woiuld also question the diagnosis on the original floppy drive as something like that is extremely rare. 

Open the Windows Device Manager, click on the USB section and uninstall ALL the entries for USB, then restart Windows and it will be detected and reinstalled (refreshed) see if that helps.

Sorry, I did all of that, but it still doesn't work. Does not recognize the external floppy drive. I have NO idea why, but can't get anything to work. thanks for your help. Any other suggestions? I thought about removing the internal floppy disk drive since they say it doesn't work. We put a new one in and that didn't work either by the way.

Did you try reinstalling the Dell chipset drivers?  That may be all that's needed to get the internal drive working again.  And, it may be a good thing to try for the external drive too.

How do I reinstall the Dell chipset drivers? It says I have the correct drivers for the floppy disks.

Try this. Restart the computer and on the blue dell logo screen, tap the F2 key to enter the setup. Turn on the num lock, scroll lock and caps lock keys. Press the alt+e keys together. You will get a beep. Press escape and select to save changes and exit and press enter. Check if this resolves the issue.

Sorry, I tried what you suggested, but that doesn't work either. Don't understand why someone out there cannot tell me what the problem is. Surely someone else has encounted this. But maybe not. Thanks for your help. Any more suggetions?