I believe I know the issue here, as I've had this done to me before.
What you need to do it head to your My Documents, which is usually found at;
My Computer >
C:/ >
Users >
[Username
] >
My Documents
After that, you will need to find the Mabinogi folder. Should be easy, as it has its own icon.
Considering you haven't done much, I would advise deleting everything there. If you have things you want to keep, like any screenshots you may have taken, be sure to take those out.
If this doesn't work, please tell me the message given to you as you crash.