Lenovo vibe K5 is not turning on anymore
In this state, flashing the stock firmware still the solution. You need drivers for the PC to detect the phone.


Click here to get the USB drivers and the flash tool.
Click here to get the flash file (firmware).


Alternative download links:


Firmware 
Flash tool
Drivers


FLASHING STEPS:


First download firmware, flash tool and/or drivers from above links.
Extract zipped files to desktop or anywhere you'd like (You'll need winrar or 7zip software to Extract).
Open Driver folder and choose  Qualcomm_USB_Driver_Setup.exe file and wait until finish installation.
Open QPST.WIN.2.7_Installer-00430.1 folder and chose setup.exe file, open and install it.
Now open QFIL from the "C:\Program Files\Qualcomm\QPST\bin" path, Select Programmer option and click on Browse button and Select prog_emmc_firehose_8929.mbn from SW Folder file.
Click on Load XML button and choose
rawprogram0.xml file and then choose  patch0.xml file from the SW Folder folder.
Press and hold Volume Up + Volume Down and insert USB cable and wait until driver install are installed. 
Click on Download button and wait until flashing process finishes.


Oh, and you may need a video tutorial to make it easier, find it here: 
Flashing process