I don't know what elase to try swanmark.
Are you sure all other drivers that use USB have been disabled? (your tv dongle, printer, camera etc.)
If you are, unless anyone else has a suggestion, I would call it a day and return for a refund.
If you wish, you can purchase an EzCAP116 from myself and try it. It has never had an issue like this and it comes with real drivers for windows7. If you try it and it does not work, (it then has to be a driver conflict) you have my word you can return it and I will give you a full refund.
They should just be plug in and go. Not all this.
Below is my ebay feedback for the EzCAP116
http://feedback.ebay.co.uk/ws/eBayISAPI.dll?ViewFeedback2&ftab=FeedbackAsSeller&userid=flix49&iid=-1&de=off&interval=0&items=100