Can not flash k750i after using update service

Pls help me ...
I have a k750i phone, CID 36 red. Before i flash to w800i and the flash it back to k750i. After 1 year, now it has problem, the light just flashing when starting, i have use sony-upadte service to to update it but it still sometime flashing? now i want to reflash it by myself but can not, Sx++ out after i press start .... , i use Main and FS for k750i - 36 red, so now what can i do , pls help me

Yeah, i can flash it back to k750i now but the light sometimes still flashing after restart phone ( when it hang ), pls give me a suggestion to solve it, tks..