... a few possible problems.

bit debounce=1;
bdata unsigned char row_no,col_no;
sbit col_no0 = col_no^0;

void delay(unsigned int itime)
{
  int i,j;
	for(i=0;i<1275;i++) <--------- Do you want to do this, or do you want the loops nested? 
		;
	for(j=0;j<itime;j++)
		;
}

		:
		:
		:
		:

unsigned char key_scan()
{
  unsigned char temp,i,key=100;
	col=0xff;
	row=0x00;
	while(col==0xff)
		;  <--------- This is going to loop forever! 
	temp=col;
	delay(20);
	while(col==0xff)
		; <--------- So is this! 
	if(temp!=col)
	{
		debounce=0;
	}
	else
	{
		delay(20);
		temp=0xfe;
		for(i=0;i<8;i++)
		{
			row=_crol_(temp,i);
			if(col != 0xff)
			{
				col_no=col;
				col_check();
				key=key_matrix[col_no];
				col=0xff;
				while(col!=0xff)
					; <--------- And this! 
				return key;
			}
		}
	}
}

Unless col is being changed in an interrupt routine that was not shown, your while loops will loop forever.

Personally, I ALWAYS put the semicolon after a while() or for() statement on a separate line. Otherwise it is too easy for the reader's brain to skip over that little mark. When it is on a separate line, I KNOW that I wanted the code to do nothing inside the loop. In fact, I use a macro: #define donothing ; to show that I really, truly do not want to do anything in the loop.

--Rich