iphone 4 was water damaged has had new battery as wasnt charging and new docking port and it comes on to apple logo now then off after 10 to 15 secs and reboots any help please

Your phone maybe damaged beyond repair. You can try syncing it with itunes and seeing what message pops up. It's more likely you will have to buy an out of warranty phone.

Help with what? Apple does not repair iPhones, they replace them. Apple does not sell parts. There are no legitimate sources for iPhone parts.

Talk to whoever did the initial repair. Odds are the logic board is damaged. It's probably time for a new phone.

Your phone is no longer eligible for a discounted out of warranty replacement.

Thanks for clarifying Tim.