(Help)Lenovo A 1000 phone flashing

Hi , I’m trying to flash my Lenovo A1000 with a stock rom after a failed root that wrecked the system completely (it’s completelyinaccessible, even the recovery) when i power up the device it shows the Lenovo logo and then hangs on , so i now i haveto use using SPD upgrade download tool (R2.10 tried other versions too) , here the problem normally the drivers are installed correctly both SPD and CDC , when iplug the device to the USB port theSCI Android USB2Serial port shows up on my device manager(some time with yello triangle and as phone displays it ok) , i start flashing it , for seconds all looks clear but then the phone opens to start (a flash on screen) the SCI Android USB2Serial port disconnects and user disconnected error on spdt. which interrupts the flash and stops everything and shows the device unplugged on SPD upgrade download toolPS: I’m flashing it with a Pac file as the stock rom. And on Windows 7 x86. Pls help to resolve.( the same pac file with the same tools i success fully flashed my friends phone 10 months earlier)