I uploaded the atmega 8 bootloader
using usbasp
then I load program using usbasp too
before that , once after burnt the bootloader,when I press reset button, the led at pin 13 blink a little while
but once loaded program using usbasp programmer, it seems like the bootloader gone
because when I press the reset ,the led at pin 13 wont blink
And when I change to USB, I cant upload the program because the bootloader is gone 
What problem is that ?
Thanks
Vincent19:
once loaded program using usbasp programmer, it seems like the bootloader gone
Yes, if you load a sketch with a programmer it will erase the bootloader. Your sketch gets control immediately on power up or reset. If you then want to be able to upload sketches via USB you have to re-burn the bootloader.
Why it is like this ??
Can it be solved ?
Thank you
Yes, load the bootloader and then load programs using the Serial or USB connection. If you load hex files using avrdude and usbasp then the bootloader is overwritten. Decide how you want to load programs. Using serial/USB using the bootloader or the usbasp and no bootloader.
Either one only ? Can it be like I can use both ways to program ? First I used us asp then later on I do not need to burn again the boot loader to enable to load program using USB cable ?
Thank you