Sc400 Wont Start

[malsc400]

Hi Im new to the forum and i have a problem with my Lexus. Its a 95 Sc400 and it does not want to start. It first started making a grinding noise when i would try turning it on. Then it would randomly want to turn off when i would go over a speed bump. Well i had a friend change the timing belt and some of the injectors for me. And i dont know if it was his fault or not but when i went to get the car back it didnt want to start anymore. My dad and me changed the starter but it still didnt want to start. Can anyone give me some advice. Cause i dont want to have to take it tp the dealer but it looks like i might have to.