My Arduino Uno was working nicely. And then something like
avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00 started to appear.
So I searched for solution and discovered that my Uno is missing its bootloader, and it can be solved. So I bought another Uno and with its help I restored bootoader of the first Uno.
There starts the main problem. Everytime I restore bootloader and try to sketch a program and it crashes its bootloader. Yes, I can buy another Uno or I already have a good one in my hand. Still, I would like to know what's happening?