No one can remotely help you there. Just attach the debugger and debug it as you would any other problem. If you do no know how to debug yet, you have to make it your single most important priority to learn it.
That said, I would advise against just turning any non-trivial x86 project into an x64 project. There is far too much that can systematically cause problems when x64-compatibility was not a design decision from the start.