Issues in a costom board Arduino Core

I have some troubles with the Arduino core board that I build.
I use an ATMEGA328PB-MU and a CP2110-F01-GM for the USB connection.
I used an AVRISP mkII from Atmel (with an external power supply)and the Arduino IDE to burn the bootloader. I don´t have any problem n that part.

When I finish burning the bootloader, immediately the LED that I connect, started to blink (Like the blink LED example), connecting with an external power supply.

When I connected directly I can see the normal behavior (The blink led behavior), but when I connected directly to the computer by USB port the blink LED is faster like if the MC enters like a programming mode.
I can´t program with the Arduino IDE.

The ATMEGA328PB-MU is directly connected to the 5V, I don´t use a LDO.

Do you have ides what is the problem and how to solved it?