As per the operator manual in the case of the picture not showing up correctly, begin by pressing the "PICTURE SIZE" button several times to cycle through the various size options (sounds like you have tried this though). Next, press the power button first
to see if it fixes the issue... if not, then press this sequence of buttoms on the remote control (6 buttons in this sequence):
"SLEEP", "PICTURE SIZE", "[right arrow]", "[up arrow]", "[down arrow]", "[pwr button]". This restores the default screen size settings.
I am not sure how you are using your monitor (TV, HDMI, Composite, PC Monitor, etc.. ). That would be very helpful.
If this does not resolve the issue, I would suggest downloading the service manual from this link to work through the advanced troubleshooting flowchart... They point to a reinitialization of the basic functions (reset the TV to factory defaults) through the initialization process. I have worked on a number of this model, and have almost always found it is settings which have been inadvertantly mis-adjusted while tweaking preferences or the last settings of the operation since it will always go back to the last way it was setup when you power it up (no matter what modality was in use last time.. eg. 480i in PC or DVD operation changed to HDTV next time). Remember the HD 16:9 screen is nearly twice as long as the old 4:3 screens, as well as having nearly twice the vertical pixels... Thisis what it sounds like in your case with the 19" screen to me.. Let me know if this helps...