Original locked thread http://www.keil.com/forum/58113/
For broken code downloaded onto a device, pull BOOT0 High, the erase the device and reset without BOOT0.
Cortex-M0 devices are SWD only, make sure not to select JTAG.
Try other connection/reset option "Connect under Reset"
Try also ST-LINK Utilities to erase and reconfigure device.