Some early HDTVs, and your HP might very well be one, have HDMI ports that only support one HD resolution: 1080i. Roku players do not support this resolution. If you're seeing the bouncing Roku logo, that's the boot screen that is being sent as an SD signal, which the Roku will display. But once it boots, it needs to be connected to a display that supports 720p or 1080p.
A quick look on Amazon doesn't show any 1080i to 1080p converter boxes, so there's likely no low cost solution there. There are quite a number of converters that will convert HDMI 1080p to component, and perhaps your HP supports that type of connection. You lose the audio doing that, but most converters include analog audio output jacks as well. Just don't expect 5.1 audio from such a converter. If your HP supports component video, there will be three RCA jacks: red, green and blue. There might be two more jacks together: red and white. These are analog audio input jacks.
I investigated the resolution on my HP Model PL4260N, Plasma HDTV. The resolution is 1024 x 768p. Should this resolution work with a Roku Ultra?
In theory, I would expect that display to accept the 720p signal. But it's possible that it is not accepted, as I mentioned before. Many early HD displays (and especially a computer display, which is what your HP likely is) would only accept a very limited number of resolutions. You may simply be out of luck with that display.
EDIT: I see that it is a HDTV, not a computer monitor. Unfortunately, the owners manual only lists the resolutions usable on the VGA port, not the HDMI port. But you have one possibility: your TV does have component inputs, so you could use an HDMI to Component converter and feed the audio out from the converter to the TV. This requires a total of five RCA cables: a three cable component set and two cable audio. But you should at least then get an HD signal from your Roku to the display.
