Did your application crash which lead to non-detectability?
For this matter, please use Hyperterminal and try to connect to the module. Now check if the module responds. Also make sure that the boot switch (which is adjacent to the reset switch)is set to off.
In case, your application is causing the module to reboot indefinitely, you need to download the AT firmware again. Please check out with your Wavecom contact person and ask him to provide the DwlWin utility. Also ask him how to use this utility.
Hope this would solve the problem if any.
Please make sure that the power plug is connected on the correct input socket. You can try changing the VBATT or 3V6 to which you have connected the power.
Also check if the boot switch (which is adjecent to the reset switch) is set to off.
In case, it still does not responds, ask your Wavecom contact person (i.e. the person who supplied you the modules) to look in this issue.
Open AT Fan.