user33638: 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 <ff> 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 

user30005: 
What if I have burnt my atmega328p?

get a new one.

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 .

based on the information you have provided, no one can tell definitively. you could have changed the fuse settings, or your 2nd chip didn't have the bootloader, or bad connection, ....
a better approach is to get a separate programmer - usbasp for low prices, or dragon (older debugger with hv programming capability) and go from there.

user7508: 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.

user33638: after two days of searching on internet, I decided to just reburn the bootloader again on my target µC to discover if it's really burned or not. 
SO, I guess it was not damaged because I was able to burn the bootloader and upload the blink led  sketch successfully. 

33638: <p>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 : </p>

<p><code>"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 "</code></p>

<p>But unfortunately it did not work well and I have got the following error : </p>

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

<p>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] [<img src="https://i.stack.imgur.com/0LFor.png" alt="PIC">]<a href="https://i.stack.imgur.com/0LFor.png" rel="nofollow noreferrer">2</a>.
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"  <a href="https://i.stack.imgur.com/bdXCI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bdXCI.png" alt="PIC"></a>
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 </p>
 30005: <blockquote>
  <p>What if I have burnt my atmega328p?</p>
</blockquote>

<p>get a new one.</p>

<blockquote>
  <p>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 .</p>
</blockquote>

<p>based on the information you have provided, no one can tell definitively. you could have changed the fuse settings, or your 2nd chip didn't have the bootloader, or bad connection, ....</p>

<p>a better approach is to get a separate programmer - usbasp for low prices, or dragon (older debugger with hv programming capability) and go from there.</p>
 7508: <p>Trying your fuse settings on an
<a href="http://www.engbedded.com/fusecalc/" rel="nofollow noreferrer">AVR fuse calculator</a> 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. <em>Then</em>
you can try to reprogram it.</p>
 33638: <p>after two days of searching on internet, I decided to just reburn the bootloader again on my target µC to discover if it's really burned or not. 
SO, I guess it was not damaged because I was able to burn the bootloader and upload the blink led  sketch successfully. </p>
