What if I have burnt my atmega328p? Actually I am facing a big problem while programming my atmega328p using an arduino uno as ISP. 
I followed a video on youtube  "Arduino as ISP" by Notes and Volts. Which look doing the same steps that the majority followed. For the blinking LED sketch the µC worked very well and it did not show any troubles. 
So I  decided to carry on , and at this point I needed to upload a new program but this i wanted to upload my program using "avrdude" command line because my code was written with MikroC pro for avr, and here is the command line : 

"avrdude -p atmega328p -b 19200 -C arduino -P COM7 -U lfuse:w:0xf7:m -U 
 hfuse:w:0xc9:m -U efuse:w:0xff:m -U flash:w:LED.hex:i "

But unfortunately it did not work well and I have got the following error : 

avrdude : invalid byte value &lt;ff&gt; specified for immediate mode 
 avrdude : write to file 'ff' failed 
 avrdude : safemode : Fuses OK

Seeing that error paniced me , that's why I decided to retry the programmation with an arduino sketch and then happened the big issue when the arduino generate an error message about finding a bad microcontroller [error about the device signature] []2.
My last try to find out if I ruined my µC is with switching the µCs; the arduino original and the one that I had to program and unfortunately It was not a good result : 
"avrdude : stk500_recv() : programmer is not responding 
 avrdude : stk500_getsync() attempt 1 of 10 : not in sync : resp=0x85"  
Looking for more than day on the internet and I could not find a valid solution , except the possibility that I really BURNT my µC and I have to buy another one. And this is specifically why I am asking for your help; I need  to know if SO could figure this trouble out.Otherwise, could somebode confirm to me that there is no hope with my µC and it's gone and I have to stop trying to make it works . 
Thank you 
Regards
Trying your fuse settings on an
AVR fuse calculator shows that you
have selected an “external full-swing crystal” as the clock source.
Now your ATmega won't work unless you connect it to an external crystal.
Or you could try just sending a square wave into the XTAL1 pin. Then
you can try to reprogram it.