Could try unisntall and reinstall the software but have a look in properties of My Computer, Hardware, Device Manager and scroll down and see if any yellow question marks present under USB controllers or if windows xp use system restore to a date it was working. Alternatively purchase a memory card reader and install this as these are much quicker than connecting a camera and usually allow you to read and write to various types of cards.
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Try fixfault.com to fix digital cameras.