why is there a horizontal line across my imac screen?

Do you see it all the time? If so, it's a display or display connector problem, but first, reset the PRAM > http://support.apple.com/kb/HT1379 Also, do a SMC reset > http://support.apple.com/kb/HT3964

If they don't work, I suggest you to take the iMac to an Apple Store or reseller

Not sure exactly which model your iMac is..?

see > How to identify iMac models

Sadly display lines generally indicate a problem with either the Display or the Graphic's Chip.

To check, take a screen shot of the display using the (Command Shift 3) keys and open it.

If the line is only seen on the Display and not in a screen shot, then it would most likely indicate a Display problem.

If the line shows up in a screen shot, then it would most likely indicate a Graphic's Ciip problem.

Hi bro,

Thanks in advance for your reply...

*If the line is only seen on the Display and not in a screen shot, then it would most likely indicate a Display problem.*

Exactly same at my macbook bro. Warranty expired. What should I replace basically ?

Thanks

Salim