electrics?

my car is a renault megane 1.5 dci 04 plate . so far since buying the car second hand i have had to have a whole new gear box , clutch etc.... now the next issue seems to be electrics three of my windows have dropped completely the motor and switches will not work at all . when i lock my car now , instead of the windows going up when you double lock the car the drivers window is going down ! ? i really dont want to be spending stupid amounts of money on it anymore but i love the car and really want it fixed . also when i try to put my foot down anything over fifty mph it says on the computer screen check injection . ........and my radio passcode has been cleared and have had to fit an extra radio because i have no way of using the one installed . All electrical problems i think please help