Something you might try... but before getting to painter I want to mention something. This happened on Mac and I'm sure it might also be the case on Win7 x64... I have to do a session to test but please bear with me. I finally bought a 6d ArtPen to add to my Christmas present an I4 medium only to find that it wasn't detected at all, even after a reboot. Having had a lot of tablet related experiences with my Geniuses over the years I went to the Wacom site and downloaded the latest drivers. Next I uninstalled them. Installed the atest drivers, logged out and back in again and hey presto!
What I might suggest you try is this.
Before you get started download CCleaner and the latest Tablet drivers.
Next having installed CCleaner use it to uninstall your wacom drivers andPainter 12... Completely (back up any custom tablet configs etc first though!
Next run the registy cleanup utility in CCleaner and maybe a history cleaner too (Option 1) You may get asked if you want to save your existing registry configuration first,,, choose whatever you like, I have never been able to succesfully repair a registry in 15 years if it goes pear-shaped so I just ignore this.Shut down your system, unplug the wacom and reboot.
Now try installing P12 again. If you are succesful with this then shut down again, re-plug yout wacom. reboot and install the latest drivers.
This kind of routine has brought me some success in the past with P 10 and 11 as well as other programs on 64 bit Windows. Failing this, like Jinny, I am not sure what else could be causing the problem other than a messed up registry entry or .dll conflict which will most likely resuly in you having to do a registry clean up. Steps for this you should find within these forums but be warned... playing about with the regisry can result in an inoperable system, so be sure you follow the guide step by step if it comes down to that, and Best of luck! I've been there personally quite a few times and reckon my success rate was maybe 70% Have lost my OS totally on at least 2 occasions. Hope things are not that drastic though. Seems as though you can install the app no problem and its just the lauch that's giving the issue.
Just on a side note, you have not mentioned your system configuration. Painter 12 is a huge memory-eater from what many have been experiencing so far. If you have minimal memory and or other apps running for example this might cause the program to hang and crash.