Q:

Nothing happens when I run program

The guys just helped me with a problem, got solved 100%, but now I have another one. 
I compile my files and everything without problems, but when i want to run the program nothing happens. 
enter.c : http://pastebin.com/GGzVeAhw
simple_interest.c: http://pastebin.com/XdESrxSk
This is how my header file looks like:
int enter(void);
double Calc_Interest(double principal, double rate, int term);
double Calc_Amount(double principal, double interest);
double Calc_Payments(double total, int term);
void Display_Results(double principal, double interest, double total, double mPay);

PS This forum is really helpful, especially for a beginner like me. 

A:

You have a bunch of prototypes in main(), but no function call. 
It should be:
int main(void)
{
   enter();
   return 0;
}

You seem really confused about how to declare and use functions, perhaps you need some tutorial?