Hello I am using the STM32L152 discovery board but suddenly is not detected by my PC. I am also using STM32F407 Discovery board but there is not any problem like this.

[PKuma.12]

So why this issue in the STM32L1 discovery board.I also uploaded images regarding the problem in the board. 

[Tesla DeLorean]

Perhaps you just broke it?

Try different cable, USB port, or on another system.

Avoid using a hub or docking station.

If it still fails and you want more answers, pull the schematic and probe voltages present on the boards and at critical nodes.​

[PKuma.12]

ST link is detected but the code is not able to load in device and getting this error.

[Ozone]

Perhaps the current application on the target (L152) "misbehaves", like going into sleep mode ?

Try booting the target into system mode, and do a Flash mass erase.

[Tesla DeLorean · Accepted solution]

Ok, so try changing the connection settings to connect under reset, or try pulling BOOT0 high so your current code load doesn't run.

Then look at your code for low power modes or GPIO configuration that might break the debug interface.​

[PKuma.12]

Thank you for the answer

Now it is working.