Compaq cq70

Hello, 1st problem started by my laptop saying battery is not powerfull enough you need to replace battery and this was just on a black screen after booting up windows 7. So after this problem I took battery out and powered up with power lead connected and then it said no boot disk available so turned off and tried again. I done this by holding the power button down for 5 seconds and shut it down that way. After leaving laptop for a while as had to go out I put the battery back in and put it to 1 side. Returning later ive powered up the laptop everything powers up the disk drive makes boot noise the hdd makes slight noise the fan is working all sounds normal on boot the power lights on wireless lights on but nothing at all comes on the screen its just blank dead looking. Only thing I think ive missed from this is that if I take the power lead out the laptop just shuts down thats with the battery attached. If u need any more info please ask and please please help thanks in advance.