My Uncle recently gave me his old C280. After having it for a couple months the car would not start would just make a whirring sound. Figured the starter was bad so I pulled it out, took the starter in to have it tested both the solenoid (fried) and the main body (seized). So I got a new one, put it in(the original mounting point for the ground strap was seized so i went to the grounding point for the transmission), reconnected the battery but instead of power got a weird scream coming from the passenger side speaker. I had the battery tested before all this due to having drained it a couple times by accident and it tested bad. Got a new battery put it in same problem. Oh and no power to any dash lights, trunk lights, or anything else however i can cause it to spark while attaching the positive strap after connecting the negative so the battery does have juice.

Does anyone have any Ideas what could be the problem here? Any help would be appreciated.