radio problem

[davidamd]

im having a small problem with my radio, it used to have some after market junk in it with a cd changer which has been removed as some wires are still there,
i put in a vw gamma it lit up on the illumination but wouldn't turn on, so i tried a kenwood thing i had, it powered up but couldn't access it as its needs a transponder to activate it,
si i then put my mfd in to test and it worked but had to take out as only a single din slot for the moment,
i then received a vw beta but same as the gamma illuminated with the car lights but wont turn on
any ideas what the problem could be,
im taking a small trip with the farm and dont want to be without music
the car is a b5 r reg passat est