USB external hard disk problem

[TanZail]

I am using a Windows XP based desktop. Recently updated it with Service Pack 2. Everything worked fine for few days but now something went wrong automatically. I have few external hard drives and Flash drives that use to be connected with this system. Since yesterday all these external drives are showing up as unknown device in My computer and device Manager.

As per troubleshooting I tried updating drivers but no help. Re-installed Service Pack 2 again, yet no success. Do anyone have any idea what is causing this problem? I check all ports and the result is same. Is there any fix for this apart from re-installing entire windows XP? Please provide some help.

[JUSTICE]

The steps i'm going to suggest you has worked for me several times with external devices. Hope it works for you as well. Click Start Button, click Run, type DEVMGMT.MSC and press Enter. Now highlight any of those device, from the menu click Uninstall. Once done, again from the Action menu click on "scan for hardware changes". Let the windows find and install the required drivers automatically. During this process make sure those drives are connected to the system.

[TanZail]

I appreciate you help JUSTICE but i have already tried that and it dint helped. After uninstalling and clicking on Scan, system finds and installs the device and drivers ans confirms saying me that "device is ready" but just after few seconds it says "USB device is not recognized."

Surprisingly the problem is only with these external flash drives and Hard drives. Rest my digital camera or USB Printer or USB adapter stick are working fine on the same Ports. I dont know what could be the problem.