More than likely, in my experience, the inverters go out more commonly than panels. Inverters are also dirt cheap and easy to swap out compared to panels. Jump on ebay and find an American supplier that has one for the dv2500. Will set you back less than $10 and give you a quick answer.
That is ONLY if you get video on external monitor. If you get no video on external, your video card might be shot. Check HP's site for recall info, I know the dv6000 had video issues, not sure about the 2500 series... Hope that gives you a good start.