No upload possible but serial monitor working

Hey folks,

I've got an arduino mega2560 clone with a CH340 chip. When I connect it to my computer I can see the serial monitor output from code I uploaded with an arduino uno via isp to that mega, so the connection is ok and the driver must be too. But I can't upload new code via usb, it just gives me a timeout error if I try so. Any ideas on how to fix this or is my clone just broken?

mzev:
I uploaded with an arduino uno via isp to that mega

You erased the bootloader.