my precision t.v ptf21r98 wont turn on/ start up normally?

hello. my 21" precision ptf21r98 t.v-flat wont turn on/ start up normally. if left unplugged for a couple of days it will turn on but if turn off for a few seconds its back to the no start. picture, sound and other features r o.k. a capacitor was replaced and it started ok but when turn off it has the same problem to start