i have tryied to update my k800i and i have failed because it doesn;t finds my phones drivers.after that my mobile didn't open again.
what shall i do?

if U interupted FW update you're in big trouble now. there are only two sollutions for U:
first, visit local SE service and tell them what U did
second, find someone who can FLASH your phone, this also can help........

first take it to where you bought it since it still under warranty and see what they can do.

Otherwise take it to a authorised repair centre to get it repaired