That happens occasionally with my capture. Disconnect your tablet and let it pretty much rest. After a few minutes, connect it to the computer again and hopefully it works. Might take a few tries sometimes but yeah. I have the same problem sometimes.
Does it not responding for touch as well? If it does, maybe theres smth wrong with the pen... Anyway- try to reset computer, there may be some issue with software, did You installed smth new lately? It may but doesnt have to cause some problems. If there are no conflicts, try to re-install tablet software. If THAT doesnt help...then i dunno