Timeout communicating with programmer

Hellow every body
I have a proplem during downloading any application on my arduino mega2560, I faced a message says:
"avrdude: stk500v2_getsync(): timeout communicating with programmer"
Using arduino uno as isp proframer, I have upgraded the bootloader. When I tried to dwonload other application through the arduino uno as isp I faced the same problem.
Now I cannot program this arduino mega.
Any help please.

are you downloading TO your arduino mega2560? or THROUGH it?

I download to mega through uno.

Well, that message says that the Arduino IDE can't connect to the board. I would probably check the RX / TX pins, solder, etc. But as, you said you updated the bootloader, I assume that something gone wrong on that process...

Have a look at this bootloader tutorial.