I have a fairly new HP dv5-1000US and the screen is almost constantly scrambling. It's almost like a vertical hold issue; kind of hard to describe. After the last few months, its gotten intollerable. You have to play with the monitor to find a sweet spot to make it work for a bit 'til it happens again. I tried plugging the laptop to my tv via HDMI and VGA, both working perfect while the laptop screen was scrambled. This leads me to believe its a loose connection and not a graphics issue. I've also posted about this on HP's support forums finding other with the same issue, but with no solutions.

Common problem and your solution, the connection of external displays, is sometimes the last resort of
any who do not wish to incur more expensive bench time, while the problem is either cured or not.

Sometimes its a thermistor problem [heat problem] and sometimes an intermittent connection problem
while other times the entire display must be replaced.

Laptops are mobile instruments that take a lot of abuse, in normal operating conditions and varying
conditions where temperature and humidity are concerned, and the display is usually the first to go.

Sometimes the problem cures itself for a time, but it is bound to recur.

Consider how important it is that this particular laptop be your only instrument, if so, and do regular
software backups and prepare for the condition that a unit over in the corner of my lab has endured
since it was first purchased by myself in the early 90's, with an external monitor attached, and nowhere
to go........OR send it out to get it fixed.