[0xDEAD10CC]

May I ask why there is no part of the code that prevents it from executing itself multiple times?

all it takes is this

Code:

void check_already_running(wchar_t *cMutexName, HANDLE *hMutex) { *hMutex = CreateMutexW(NULL, true, cMutexName); if(ERROR_ALREADY_EXISTS == GetLastError()) ExitProcess(NULL); }

ExitProcess takes a UINT as a parameter, not a pointer type -- NULL.