Not sure of your radio, but usually the preset buttons are used to enter the code. If they're rocker switches you should be able to rock them one way or the other to reach the correct number, then the next one will enter the next .
when you turn on the radio , is the word 'CODE' displayed , or 'error' ? IF 'code is displayed , turn off radio , then with one hand hold down the#1 & #6 buttons at the same time. Keep holding them down while turning on the radio.....then let up and the serial # should appear (may show UXXXX then followed by a LXXXX ,ignore the 'U' & 'L' , write down the rest in order displayed.., that is the serial # . bring that to a dealership with car or other proof of ownership and they should be able to give you the five digit security code m which will (if correct)unlock the radio. Keep the # handy for future reference.