We have a HP f2105 monitor that that does not detect signal but detects when cable is unplugged. when we switch montiors the new monitor will work with no problem.

Beverly, F2105 unit will need to be disassembled and new momentary tactile switch soldered in. Check out ALL the different styles and sizes to choose from at digikey.com !!! at least 16 pages of switches to choose from. Then you will need a soldering iron, solder wick, solder, and know how to disassemble unit to replace a $2 to $6 switch. If contracting out the work to competent technician your looking at minimum $45.
Forget fixing the plastic button. Crazy-glue only option there.
12fixlouie

Where the cable is plugged in, a terminal probably came loose internally. DO NOT ATTEMPT TO REPAIR THIS YOURSELF! There are very high voltages inside. Buy a new monitor or take it to a repair shop.

Do this to check if your monitor is in working state or not...!

Step 1:- Turn on your computer.
Step 2:- Unplug the Video Cable of your monitor which is connected with the computer.

( Video cable:- Cable going from the back of your monitor to the back of your tower. It has a plug with two screws on the plug ends, which you can unscrew to unplug it. Thats how it looks like. Some times it is in grey in color some times in blue.)

Step 3:- Now check on your monitor. If the display says " No Input Signal " :- your monitor is fine. Some thing wrong with the computer graphics.
If there is not display and the monitor light is blinking or solid the monitor has gone bad.

( Note :- Remember when you unplug the video cable do not unplug the power cable of the monitor. )

Let me know if it helps.

It will display 'no input' if it does not detect video signal from your PC, first thing to check will be the VGA cable, check both ends to make sure they are plugged in securely at both ends. The problem can also be in the video card in the PC, but before opening up the PC, you should try this monitor on another PC first. We need to narrow down the cause first.
This is what inside your monitor if you are going to DIY repair: http://s807.photobucket.com/albums/yy352/budm/HP%20F2105/
Common problem with this model is failed LCD panel, the backlight lamp assemblies go bad or the LCD controller board goes bad.

That's normal with some monitors when they do not detect a signal from the video card.

Make sure the cable is firmly plugged in.

Monitors go to sleep when there is no computer activity it detected. Also, when your OS is working and somehow you have set a "sleep" time, then the monitor goes to sleep at the appointed time. Just press ENTER or press the POWER BUTTON to bring it back to life without losing your computer work.

try a new cable - if the issue isnt the cable then u may have a bad monitor

Sounds like your monitor is not processing the resolution signal from the graphics card. Reboot the computer in "safe mode with networking", from there you can play around with the resolution, start low resolution and work your way up to test the monitor.

Have you recently installed a new video card? If not then you need to because the one you have is broke. If you can plug in another screen to see if that works and if it does then you should re-install the software (if any) that came with the new screen. If you need anything else please let me know.

if the monitor goes into standbye when you plug it into the computer , it generally means there is NO signal coming from your video adaptor.
Plug the old monitor in , if it works, ide suspect the new monitor(s) are not working correctly.
if it doesnt work , you need to restart the computer in safe mode by repettitively tapping the f8 button as the computer starts, before it says "starting windows".
If you have a signal on your monitor in safe mode, then most likely you have a bad or corrupted video driver and it will need to be updated.
if you have no video in safe mode , you will need to remove the cover and physiclly check that all add-in card power cables and memory chips are squarly seatied in there slots. MAKE SURE YOU UNPLUG THE COMPUTER AND DISCHARGE ANY STAIC BUILDUP IN YOURSELF BY GROUNDING (TOUCHING) SOMETHING METAL BEFORE YOU TOUCH ANYTHING INSIDE THE COMPUTER.

AFTER YOU CHECK THESE THINGS AND TRECONNECT THE POWER AND TRY TO START......POST AGAIN HERE