[Q] Help With Flash Mode in Z1 c6902 topic

I had downgraded my phone from the latest update to .638 to root my phone and i lost my imei number, so my phone no longer read my SIM. So i rooted my phone using Vroot and downloaded .108 Firmware to Update back to a newer version . But now my phone no longer goes to flash mode. whenever i try connecting my phone with the usb and volume down button , the phone starts charging . the phone boots up and shows the amout of charge left. i did try with full charge :|
Please Help :/
It did work properly before, and usb debugging is on and unknown sources too. and the device is connected in MSC and SD is removed ^_^ and all proper drivers are installed too
Thanking you in advance :)