Arduino severino problem, working slow, no serial communication

I just assembled a arduino severino board. I am quite a newby in microcontrollers but not new in electronics. Apart from a severino I have a Nano, which is working perfectly. With the severino, I was able to upload the bootloader, and via ISP I was able to upload a sketch (after finding the .hex file in the temp folder). I could not get any serial commucation. What seems strange is that the clock on the arduino is not what it should be. When I have a delay of 1s in the blink sketch, the accual time is more like 5s. This makes sense to me that then also the serial port is not able to communicate. Does anybody have an idea what could be the problem and how to solve it?

If you measure carefully and find that the 1s is actually 8s it probably means that the fuses didn't get set properly and your chip is still running at the factory speed of 1 MHz.

When you 'uploaded the bootloader' did you use Tools->Burn Bootloader in the Arduino IDE? That sets the fuses for you.

Thanks. This could be possible, yes. I didn't know I should set the frequency. I did it in AVR, arduino was not able to recognise the programmer (or I don't know where to set the com port for the programmer).

Now I messed up with ISP frequency and it looks like I killed the microcontroller it's not responding anymore.