Car Won't Start, I Am Lost
 

Okay, so a little background. I bought a 1998 SLK 230 at the beginning of summer, we bought in and within the week the transmission went out. So we decided to pick up a used transmission. Installed the new one and now car won't start. Now, the car will start every once in a while but not consistently at all. The car is turning over and the battery is not dead. I have checked the MAF sensor, checked the ground cables, and checked for fuel. The car was getting fuel. I had read that pulling the battery cables for 20 mins will reset the cars computer so I did that and it started up. Then I shut it off and now it won't start again. I didn't check for spark because it must have to have spark because the car does start on some occasions. I just ordered a code reader to see but there is no emergency light. I have reset the cars computer after every change I have made just in case. Any help will be greatly appreciated! Thank you!

Sounds like an immobilizer issue to me. however, if that were the case you wouldn't be getting fuel as DAS2 cuts fuel.?? unless 98's used a version that cuts ignition.

I would check your electrical connection on the transmission and make sure it is clean and tight, i have heard that to cause issues.