Could be a number of things. Test it on another console ie xbox or ps2, even if it's a non ddr game you can see if it's your usb connector.
If you have a friend with the same pad or an afterburner pad try their control box. (if your pad has a control box.. i forget if ignitions do or not.)
if it's under warranty contact the guitar hero store. Otherwise might want to hunt a new one down on ebay or craigslist or something, if everything else fails.
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