If you wish to rotate your LCD screen there are a number of factors to consider.
Some screens are not designed to run in portrait.
Domestic televisions for instance are not designed to run in portrait and doing so would usually void the warranty.
The reason fro this is due to the thermal management design, as the units are vented in a way to vent out the top of the screen.
Rotating them can trap heat and significantly reduce the lifespan of the screen.
Another factor with domestic televisions is they often have asymmetrical bezels and look strange in portrait because of this.
Rotating your panel
Most commercial displays are designed to either operate in portrait or landscape.
Typically screens will be designed to rotate one way and not both, this again is due to the thermal management design.
Please note, panels will generally have to be rotated in a specific direction (clockwise or anti-clockwise).
Please consult the manual for your panel to determine the rotation direction, and if there are any other special considerations for rotating your panel.