Please don't expect people to download your entire project to debug it for you. It's rude.
When you are asking for help, it also helps to post the exact, complete error message you're getting as well (and especially with C++, make sure it's the first error, as often later errors are caused by the first error because parsing C++ is hard). In this case, the number (LNK2109) is sufficient for me to tell what the error generally is (via the documentation). But not the specifics.
What this linker error means is that you've declared the existence of some symbol (typically a function), but never defined it. Thus, when the linker goes to assemble all the separate object files complied from your C++ code, it cannot find the definition of function you're calling (or in general, the symbol you are referring to).
What is the specific unresolved external symbol the error is referring to? And where in your code have you defined it?