I got a convertible TabletPC HP TC4200 for some months now (I have to tell you how far this machine is *great*) and I had an issue for some days with the pen. I couldn’t use the pen anymore, as it was de-activated, although all the drivers were present. I have solved this issue by installing the original wacom driver (the TC4200 is using a wacom pen). You can find this driver here.

Back to full productivity (in fact, I have a day-off today :-).