Turned my laptop on this evening and it won't boot up. Power light and AC light is on, no hard drive light. Caps and Number lock lights flash once every 4 seconds or so, no other pattern. Have tried removing battery and replacing, no luck, held power button down, again no luck. Husband and I both have the same make and model laptop, so swapped battery and power cable, no luck, lights still flash and laptop won't start up. Please help.