You likely used "Download Only" without formatting. Reflash using . Alternatively, boot into recovery (Volume Up + Power) and perform a factory reset post-flashing.
Reviving a device that no longer powers on due to a corrupted operating system. symphony l270 flash file without password
Using the wrong flash file version can "brick" the device (render it unbootable). Always verify the hardware version by checking the sticker under the battery before downloading a file. If the phone does not turn on after flashing, you may need a different version of the firmware specifically matched to your device's motherboard ID. You likely used "Download Only" without formatting