Citroen Xsara Picasso radio dead

If you don't have manual or fuses not marked on fuse box / lid , you will have to check each fuse , one at a time .

is the battery voltage ok as sometimes low voltage/flat battery can bring on a warning light,get a diagnostic done to check fault codes,as for radio check all the fuses and make sure you are getting permanent live,ignition live and earth at radio wiring connector

I had a identical problem on my citroen xsara Picasso diesel.
My brother had recently changed the clutch and had to remove the battery -so straight away I thought it was the computer needing a re set.
So I removed the battery terminals earth first of course and then after 4 hours I refitted the terminal connections-live first on the reverse to avoid sparks (battery is located under the passenger seat on my 02 model.

OK I followed the procedure ie turn the ignition on without starting the engine leave on for 10 seconds then start engine.

Radio still not working, no sound ,no nothing.
Before starting work,remove the battery terminals as before.....

Decided to check out any fuses at the back of the radio-there are two plastic caps covering two torque screws then the radio can be removed
I noticed the front cover was loose at one side when removing on- further inspection I noticed the facia had broken away at the side
at a screw hole, rather than buy a new facia which is one option,I repaired the broken plastic and refitted the screw .
Replace the terminals on the battery and use same procedure as before
before starting-very pleased it works perfect