Posted on April 08, 2012 at 18:36Hard to say, but NRST being held low doesn't sound good. JTAG and SWD can fail if the pins they use are reconfigured, but without looking at the code, or debugging, I'm not going to be able to give a specific cause. You could also have damaged the board, or have a problem with the regulators, again hard to know without doing some measurements.
If the problem is with your code setting up pins wrong, you can always try pulling BOOT0 high, and allowing the device to restart in the System ROM loader. JTAG connectivity can take hundreds, or thousands, of cycles to wrestle control of the CPU after reset, if your code interferes with that you might not be able to get control, and therefore using the System ROM is an effective/safe way of getting control, and then erasing the errant user code.
