If your fully-charged e-cigarette battery flashes when pressed, there may be a 'short' occurring or the protection measure to prevent the battery from shorting is being activated. This can be caused by liquid on the thread or the clearomizer being on too tight. If this is occurring the first thing to do is wipe the threads of the battery and clearomizer, reassemble and then try again. If that doesn't work, try loosening the clearomizer a bit and see if it fires. You need only loosen it ever so slightly at first, then keep gradually loosening it until the light stays solid.