DIAGNOSIS The three-beep error on these models is a carafe presence sensor failure. The machine doesn't detect that the carafe is in place on the warming plate. Either the sensor is dirty, or the carafe itself isn't triggering it.
FIX First, clean the warming plate and the area around it thoroughly. Coffee spills can gunk up the optical sensor (a small lens) or the mechanical switch (a small plastic nub) located on the warming plate platform. Use a damp cloth and then a dry one. Also, check the bottom of your glass carafe. There's a specific ridge or pattern that must align. Make sure it's not cracked or covered in residue.
IF THAT DIDN'T WORK The sensor itself might be broken. It's a small component mounted under the warming plate. You'd need to remove the plate (usually held by clips or screws from underneath) to inspect it. If it's a mechanical switch, see if the nub moves freely. If it's optical, check for damage.
HEADS UP Don't try to bypass this by taping down the sensor or using a different carafe. The sensor is a safety feature to prevent the machine from pumping boiling water off the warming plate and onto your counter.