Hi Arshes Nei,
I had the same problem. If you open up the Task Manager, and look at the Processes tab you'll see that Sketch Pad actually starts and then immediately shuts down. I'm sure this happens because you installed the trial version from Corel, and it is past the trial period time. Uninstalling it leaves some registry keys. What is happening is that the Wacom version of Sketch Pad sees the old keys and sees that the trail period has expired. You need to remove these keys in order for Sketch Pad to work.
I hesitate to share my solution but if you know what your doing here's how I fixed it. You need to edit the registry. If you don't feel comfortable doing this, Don't Do It, you can screw up your computer big time. And it's always a good idea to backup the registry first before making any changes.
First install, then uninstall the Wacom version. Next install and uninstall the Corel Trial version. This ensures that we have a consistent starting point.
What we are going to do is remove some, but not all the Sketch Pad keys in the registry. We are only concerned with the keys and its branches that are involved with timeout function from the Trial version. We want to remove the complete branch though, not just a single key within that branch (which could cause unknown problems). There will be other keys that reference Sketch Pad, but they won't fix your problem and may/can lead to other problems.
Next edit the registry, and position to the start of it. Do a find (control F) for Sketch Pad . There will be several instances of it. (Use F3 to go to the next instance). What your looking for is a key and it's branches under Corel. If you have any other Corel products like Painter, they will be listed there too. Remove the complete Sketch Pad branch. Keep looking (with F3) for the next instances. DO NOT remove any keys that may list Sketch Pad but are part of programs, for instance, I use Comodo firewall and there are several policy keys for Sketch Pad listed, leave these alone, they will not fix your problem and may cause many more. There will be other Sketch Pad keys for other programs but again leave them alone.
Now reinstall the Wacom version of Sketch Pad. HTH.