Just got and HDMI cable and hooked it up to my HD cable box. It keeps on flashing onto a green screed every once in a while is that normal when you first hook it up?

screen*

NO.
What resolution(s) are you sending to what male/model of TV or display over HDMI from what make/model cable box?
Does the problem happen with both SD programs and with HD resolution programs?
Prior to getting the HDMI cable were you using the component interface without problem?

I know this is probably a simple thing, but is the HDMI cable securely and fully connected? If it is a little loose that can happen.

Just got and HDMI cable and hooked it up to my HD cable box. It keeps on flashing onto a green screed every once in a while is that normal when you first hook it up?
Definitely not.

While there is often a short delay when you switch between sources or channels that are at different resolutions, it sould only be at the moment of the switch. If you're seeing it while watching programming, it's likely a cable issue. It's either loose (as noted above) or a bad cable.

I had the same issue when I first connected my DVR (my TV goes blue instead of green). I swapped the cable out with another and the problem went away.