Multifunction display on my 2003 peugeot has messed up since friend fitted stereo.. how do i sort it out?

nothing new really has been done apart from the original stereo being taken out and a new one fitted in which didnt need any other wire adaptors and also put new speakers in doors.. which we did cut the wires to but still used original wiring.. we didnt add any new wiring... now since we fitted the stereo the date disappears and the time although when you switch the engine on comes on it stays at the same time and also it said the left door was open when it wasnt..... can anyone please help me as i have googled it and havent come up with a solution.. many thanks.