My external monitor suddenly has a blue tint

if the pc is turning on and not the display you could have a video card failure it is fixible and might cost you about 150 or so

If you connect a external monitor is it still blue? If so, Your Graphics Adapter may be bad. Try booting to safe mode, any change? If so, your driver may need to be reinstalls, sounds like a bad Graphics Adapter. Does it Overheat? Have you cleaned the fan, vents, heatsink? Any damage?

reattach the cables on monitor and pc

Have you tried replacing the cable first, I had a similar problem with my monitor(only it was blue tint). I would also check and see if the monitors connections are hooked up properly. I hope i could help.

Blue tint (Red tint, or Green tint) is more likely due to one of the pin on the VGA cable is bent ot the cable is not seated properly of the the video card conectors may be the problem. Try it with another PC and check the pins.
LCD monitors usually fail after about two years due to bad caps.

Basic LCD monitor and LCD TV troubleshooting guide:

http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting

http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

Failed TV, Monitors, Caps : http://s807.photobucket.com/home/budm/allalbums

Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Capacitor kits: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.
Please post back what you find

You are missing Blue signal, check the VGA cable and all the pins at both ends, try it on another PC also.

http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net

Check the color settings in the on-screen menu. You can choose between "Warm", "Cool" and "User". Maybe you used the "Warm" setting before and somehow it got changed to "Cool".
If this is not the case, you can try the "User" mode and reduce the intensity of the blue channel.
If even black areas show a blue tint, maybe running an auto configuration from the menu helps.
As a last resort, use the "Reset" menu item which resets all settings to factory defaults.

Compaq presario f730US notebook doesn't have an inbuilt microphone. It employs a connector (port - 3.5mm jack) to connect an external microphone.

reference : link1-cnetreview
link2-compaq
link3-Buy.com

Looks like u have lost one or more of the color channels (RGB) make sure the video cable is plugged in securley (both ends computer and monitor) and locked down with the screws, restart the computer and monitor.If this fails check video card and then monitor, can u plug the monitor into another computer this will determine if the monitor is ok or not. If monitor is ok then problem most likley will be the video card.

The screen is on it's way out I'm sorry to say. The way you can verify this is to hook the screen up to another computer and check to see if the tint is still there. If it is the phosphors in the monitor have died out and it needs to be replaced. Is it possible that it's still under warranty?