HP Support > HP 450 Notebook PC > Manuals downlaod page >http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&lang=en&cc=us&docIndexId=64179&taskId=135&prodSeriesId=5224999
Scroll down to the subheading - User Guide
Click on the appropriate Windows operating system you are using,
Windows 7, or Windows 8.
Both User Guides are PDF files.
The computer you are using now has Adobe Reader on it, which uses PDF files.
Allow the PDF file to download all the way.
Then go to the Top Left corner, and hover your mouse cursor on it.
You will see > Toggle Sidebar < will briefly appear.
Left-click on Toggle Sidebar
There will now be two icons;
Show Thumbnails on the left, and Show Document Outline on the right.......
Click on > Show Document Outline.
Scroll down the list. Click on the subheading >
Using the action keys.
(The Action keys are the F keys at the top of the Keyboard.
F1 through F12)
Here we see you hold down on the Fn key, (Bottom of Keyboard, second key from Left); and AT THE SAME TIME, tap on the F3 key. The F3 key is the Increase Brightness key.
Does not work?
Then you have a problem with the Backlight, in the LCD screen.
A primer before I go on........
An LCD screen does not produce light. It needs an additional light source.
A Backlight is the additional light source.
A Backlight can be a CCFL, (Or more than one), or a series of LED's.
(Light Emitting Diode)
A CCFL is a Cold Cathode Fluorescent Lamp. (Bulb)
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.
CCFL backlighting uses a Screen Inverter.
LED backlighting GENERALLY does not use a screen Inverter.
(First models with LED backlighting seemed to use a screen Inverter. Newer models do not)
Your HP 450 Notebook PC uses LED backlighting.
Here we can see an LCD screen replacement example,https://www.laptopscreen.com/English/model/HP-Compaq/HP~3115m~E-450/
NOTE -> Backlight type: LED
It does NOT use a screen Inverter.
How do I know? I'm looking at the Service Manual right now.
(I use two monitor screens)
You can also look at the Service Manual. It's Free, and available in the Manuals download page where you started.
On the Manuals download page, scroll down to the subheading >
Service and maintenance information.
Click on the blue >
HP 450 Notebook PC and HP 455 Notebook PC - Maintenance and Service Guide (26 Apr 2013)
Page 31 - Display assembly subcomponents
The LED backlighting is built into the LCD screen.
To replace the backlight, you replace the LCD screen.
Need step by step guidance with this, please post back in a Comment.
Hello from the USA.