I don’t have the same system configuration as you to test but the fact that the debug was working before make me think that maybe :
- The previous debug session is not well terminated, kill the “openocd.exe” process from the Windows task manager if it exists
- The ST-Link/V2 is still busy, unplug then replug it.
Then relaunch the debug session.
If it is still not working, try to connect your the board with “STM32 ST-Link Utility” ? If you can’t, it might be a hardware problem.