Power off your device completely. If possible, remove the battery (if it's removable) and reinsert it.
MSM8x39DownloadTool.exe is an executable file that appears to be a part of the Qualcomm HS-USB QDLoader 9008 driver package. This tool is typically used to flash firmware or stock ROMs on Qualcomm-based Android devices. msm8x39downloadtoolexe work