Don't assume. Diagnose.
Problem could be graphics chipset, Video Cable, screen Inverter, or LCD screen.
1) Laptop OFF, monitor OFF, connect a VGA monitor to the VGA port, on the laptop.
(Back of laptop - Blue)
Example of a VGA Cable, and a VGA connector, (Port on laptop),http://en.wikipedia.org/wiki/VGA_connector
If you have a CRT type of monitor (Looks like a small TV), you can use it, or a flat LCD screen monitor with a VGA cable.
The Toshiba Satellite P105-S9722 Notebook PC, also has a DVI connector on the back of the laptop. (Next to the blue VGA port)
You can connect a flat LCD screen monitor with a DVI cable.
Example of a DVI Cable, and DVI connector,http://en.wikipedia.org/wiki/Digital_Visual_Interface
2) Turn the monitor on. If a CRT type allow it to warm up.
Turn the laptop on.
By factory default the display should be on the external monitor.
Press, and hold down on the Fn key, (Bottom left), and tap once on the F5 key.
The F5 key is the Display Toggle-Over key.
You will see a list. It 'hot cycles' through the list, until you come to the external monitor device you are using.http://shop.mcccomputers.com/network-modem-cards/6037-toshiba-satellite-p100-p105-p105-s6104-p105-s9722-video-board-256mb-ts15082.html
External monitor display shows no white screen?
Your graphics chipset is good.
Go on with the diagnoses.
Problem is with the Video Cable, or in the Display Assembly.
(Screen Inverter or LCD screen)
The Video Cable attaches to the motherboard under the Switch Cover, and about at the F2 and F3 keys.
It then routes under the left Hinge, and up into the Display Assembly.
From there it connects to the screen Inverter, and back of LCD screen,
Due to normal opening, and closing of the laptop, the Video Cable may become pinched, and pulled on.
This can lead to a simple loose connection of the Video Cable TO the motherboard, or TO the back of the LCD screen.
(The screen Inverter connection should also be checked)
Visual inspection will NOT do. You need to physically see if you can plug the motherboard connection, and LCD screen connection in.
It could be just loose enough you won't be able to see it, but will affect the display.
Sheath of Video Cable needs to be visually inspected for signs of damage. Signs of damage to the sheath, may also mean damage to the tiny wires inside the sheath of the Video Cable.
Assurance that the Video Cable is not the problem, means checking out, or have checked out, with a multimeter set to OHM's, to run a continuity check of all the wires.
('Mom and Pop' computer store. See if they will check it)
Or simply replace the Video Cable. (After you fire up the laptop, and see if loose connections was, or was not the problem)
(Left side connects to LCD screen. Right/Top connector goes to motherboard. Right/Bottom connector goes to screen Inverter)
Video Cable checks out OK?
Go on to screen Inverter.
The plastic thin frame in front of the LCD screen, is the Display Bezel.
The screen Inverter is behind the Display Bezel, and mounted at a location towards the bottom of the LCD screen frame.
A screen Inverter is tested with a sensitive multimeter. Read fairly expensive,http://www.fonerbooks.com/test.htm
It is for this reason that those who do not have access to a sensitive multimeter, usually just replace the screen Inverter.
(Also low cost, and ease of access to replace)
Screen Inverter checks out OK?
Problem is the LCD screen,
For additional questions please post in a Comment.
[ Bet it's the video cable, or screen Inverter, that is the problem ]
An LCD screen cannot produce light by itself. It needs an additional light source.
A Backlight is the additional light source.
A Backlight can be a CCFL, (Or two of them), or a series of LED's.
(Light Emitting Diode)
The Toshiba Satellite P105-S9722 Notebook PC, uses One CCFL for a Backlight.
A CCFL is a Cold Cathode Fluorescent Lamp.
Similar to Fluorescent lighting used in homes, and businesses, but on a MUCH smaller scale.
Average thickness is 2mm. That is a little larger than 1/16th of an Inch.
Average length is almost as long, as the LCD screen is in height,
A CCFL contains -> Mercury, just like Fluorescent lighting used in homes, and businesses.
A screen Inverter is used to convert the power from the laptop, for the Backlight, and LCD screen.
90 Percent of the Time the fault is a bad screen Inverter.