my imac has a blue tint on the screen. i don't know what happend. is the screen going or can it be fixed? please help

It depends. Check your System Preferences-Displays and
be sure that under the color tab, your profile is set to iMac
Display. If that doesn't correct it, in the same preference
pane, look for a button to reset the display to the factory
default...

If all of that fails, try resetting the PRAM (restart and hold
down the command(apple)-option-"P"-"R" buttons on the
keyboard and listen for the startup chime 3 times...
release the buttons and allow the computer to reboot
normally.)

Also try resetting the NVRAM. Restart the computer and
hold down the command(apple)-option-"O"-"F" buttons.
when a gray screen wih some writing appears enter the
following:

reset-nvram (press the enter key)
reset-all (press the enter key)

Let the system resetart and see if it is corrected. If not,
take it to an Apple Store or buy a new screen. Normally
the old iMacs start to turn green, but every one in a while
they start turning blue or red... it is just getting old and
wearing out.