1. Unplug antenna cable from radio.
in "emergency antenna", typically a magmount or clamp mount about 19" tall with a dozen feet of cable on it, sold in a plastic tube.
3. Test radio.
If it works--you need to replace the coax and/or antenna. If it still doesn't work, your radio has something blown in the receiver circuit, and needs repair/replacement. Considering that repair labor can run $75-125 for the first hour...replacement, unless you can open it up and find something subtle and obvious, like a cold solder joint that is easily repaired.
You can also make a jury-rigged emergency
antenna very easily from a piece of coax with just the radio connector on one end, i.e. ten feet of an old cable. At the cut end, make a slit 1/2 meter long in the outer insulation--not the braid. Peel off the insulation
, then peel the braid back OVER the outside of the cable, keeping it intact as a tube around the cable. If you can't do that, just slice off another 1/2 meter of cable--a bit longer actually since it will change in length, and slide the "tube" of braid over the outside of the cable, then solder it together at the "turned" point.
Put a loop or tie a string to the top end, so it can be hoisted or hung vertical.
You've now got a length of cable with a radio connector at one end, and a metal "tube" near the other end. As long as the "tube" and the center section that was under it are both about 1/2 meter long, you'll have an effective antenna. AFAIK this is properly called an 'end fed coaxial dipole' and often confusingly called a "bazooka" antenna, which is something entirely different.
The radiation pattern and gain will be somewhat different from a marine
antenna--but this is perfectly matched to your radio and perfectly good for testing and emergency
use. The 1/2 meter measurements aren't dead on, if you have an SWR meter and a few formulas you are welcome to tune the antenna more precisely. But, it is a cheap
way to have a working antenna for radio testing. And easily stowed.