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A crack in the digitiser will cause the screen to stop responding, the only other cause can be a damaged digitiser ribbon.
The bad news is that digitiser replacement is expensive and sometimes uneconomic. A new touchscreen will cost $99, a full screen replacement - $149 (
www.pocketPCtechs.com). At these prices it is almost the cost of buying a replacement X5 from ebay or such and 50% the cost of a new x51
