http://www.prgr.com/support_faq_crt.htm#out_of_range

My monitor showed "PLEASE CHECK SIGNAL CABLE." What does that mean?
The monitor needs to measure the horizontal sync frequency to determine which of its presets to match the resolution format to. The most common reason for this message is that the sync signal is missing. You need to do the following:

• On monitor models with dual inputs, make sure the monitor input select switch is in the proper mode for the channel you are using (refer to your manual)
• Check the pins on your signal cable to see if any are bent, broken or pushed in.
• Verify the video card is putting out a valid signal by substituting another monitor, or taking this monitor to another PC. Even if your PC appears to be booting up by the indication of floppy or hard drive activity, the video card may not be putting out a signal.

Other on-screen messages on various models related to this discussion are "SIGNAL MISSING" , "NO SIGNAL" and the tri-color "SELF TEST."