PC does not detect any USB mass storage device

[Quique]

Recently i have bought a Fujitsu External Hard drive (externally powered) which has 40 gb capacity. It was working fine but suddenly my computer is not detecting any mass storage device. I use Windows XP Service Pack 3 on my computer which i think is the root cause of all the problems. When i use the external hard drive with an external source it gets detected but i cant access the data also if i connect the HDD using the USB cord only then the HDD does not show up. Please help
Following is my configuration. Intel core2 quad 2.2 ghz, Intel DG35 motherboard with 6 USB ports. 4 gb ram. Windows XP service pack 3

[Bon-Z]

The USB portable drives are very unreliable. They are more prone to getting damaged or corrupted easily. Test your hard drive for any physical damage which could have made it faulty. Hard drive Diagnostic tools are available which check the hard drives for errors. Use them to be sure of the reason which is causing such problems.

[Deep23]

Windows Xp with SP3 has many problems with compatibility. Many devices do not work properly with Windows XP sp3. I suggest you to format and change the operating system to Windows XP sp2 which is more stable. If not then find suitable drivers for your hard disk so it can function properly with the installed Operating system.

[Lambard]

As your hard drive is detected when connected to an external power source but cannot be accessed, there must be a problem with the data cord connecting the device and the computer. USB cords are made up of many conductors known as lines. These lines tend to get faulty due to corrosion or wear and tear. Try connecting the hard drive using another USB cable and check if the problem persists.

[Halina]

The problem is with the USB ports of your computer. They are not able to power up the hard drive properly. Check the USB ports by connecting different USB devices and check if they work properly. USB ports on your computer have probably gone bad. USB devices like Mouse and keyboard would work properly but data storage device wont work as they require more power. Replacing the motherboard is the only solution.

[Wiro]

Test your external drive by connecting it to the computer which you know is good. If it works fine then there is possibility of Virus present on your computer which is not allowing you to access any mass storage device. Scan your computer with a UPDATED antivirus and clean the infected files. Then try to connect the device which i am sure will be detected.