Hi @Priyanka23 ,
When you meet this issue, your flash downloaded code may not complete or valid, so it cause the boot issues, then it may also influence the on board debugger connection.
Now, follow me to recover it:
1. SW7 1-OFF, 2-ON, 3-OFF, 4-ON, power on the board again.
2. download your SDK helloworld code again, you may see can't enter debug successfully, but not important, just wait download finished. Then exit the debug mode.
3. power off the board, SW7: 1-OFF, 2-ON, 3-ON, 4-OFF, then power on the board again, then debug it again, it should work now.
Please try it on your side.
If you still have issues about it, please kindly let me know.
Best Regards,
Kerry