I have a leak on my radiator and replace it, after this my car won't start! Please help!

Check your Radiator Cap

Did you put coolant in it? Did it overheat? If it was leaking and you replaced it maybe its too late. An engine needs to stay cool to run. Thats what the purpose of a radiator is for. But if you drove it when it was over heated then it goes from replacing a radiator to replacing an engine. What was the vehicle doing to make you replace the radiator?

With the engine off and cold, open the hood and locate the vehicle's radiator and water pump. Remove the radiator cap.Install a pressure tester on the radiator. Apply the pressure indicated on the radiator cap or in the owner's manual. Inspect the water pump for leaks. Remove the pressure tester. Place a drain pan under the radiator. Open the drain valve or remove the lower radiator hose to drain the cooling system.-----------------------------------------------------------------------------------
CARPROG FULL V4.01

possibly a heater hose leak or maybe a freeze out plug

I don't see how leaking transmission fluid would be connected to the engine overheating, unless the radiator blew up.
You'll need to figure out why it won't start to proceed.
Check for spark and fuel pressure, and of course compression.
Is the check engine light on ?

you said it cranks then you said it wont turn over if it wont turn over you might have get the engine to hot and seized the engine please spesifiy if the engine turns over or not

I suspect you have very little experience or
confidence, in you ablities,based on the question

There is no step by step for most auto maintenance
& repairs.

Just have to get in there & start figuring it out

I know you want to save money & avoid a repair
shop bill,I'm sensitive to that,but instructions, if
avail, won't give you the apptiude to reason out the how
to do it

Lift the hood. In the upper right hand corner is the overflow fill tank. If you want to put it in fast reach down the right side of the radiator(when it's cool) unscrew the small plastic petcock and drain a gallon or two of antifreeze into clean pan. Replace petcock. Open the cap on tank and add stop leak. Fill back up with antifreeze. Now would be a good time to change it. Go to Napa and buy the original antifreeze the car came with Zerex G5. Mix 50/50 with distilled water.Fill to just above cold line and start engine keep adding mixture till it won't go down any more. Replace cap and watch level for two or three days of driving add mixture after engine is cold

Hello robtui: My name is Roger and I will help with your problem. The engine cranks over and does not start? Collant is belched out of the radiator? Problem is a warped head(s).Blown head gasket or cracked head. Remove the spark plugs fill the coolant system and you should see coolant fill and run out a spark plug hole. The engine should of had a miss before this happend. You could also do a compression test instead of filling the radiator and looking for coolant to run out. Either way you will find a cylinder compression leaking to the coolant passage. Should you need further help please just ask. Please rate the answer. Thank You for using Fix Ya. Roger

your radiator is probably bad small leak but itll do its deal of leak...