STM32F103 GPIO not working
Here is a simple program that should help:

/* main.c
** Simple program for Olimex STM32-H103 (STM32F103RB) to flash LED on PC12
**
*/

#include &lt;stm32f10x.h&gt;

void delay(void);

void main(void)
{
  // I/O port C clock enable
  RCC-&gt;APB2ENR = RCC_APB2ENR_IOPCEN;
  // Set PC_12 to output 
  GPIOC-&gt;CRH &amp;= ~(GPIO_CRH_MODE12 | GPIO_CRH_CNF12);
  GPIOC-&gt;CRH |= GPIO_CRH_MODE12;

  while(1)
  {
    GPIOC-&gt;BSRR = (1&lt;&lt;12);
    delay();
    GPIOC-&gt;BRR = (1&lt;&lt;12);
    delay();
  }
}

void delay(void)
{
  volatile unsigned int i;

  for (i = 0; i &lt; 20000; i++)
    ;
}


It was written for the Rowley CrossWorks compiler.