I have attached a new cdrw in my pC but it is not getting detected . whenever PC is starting LED is getting on for few times .
If your using IDE cable for CDRW, then:
Maybe the CDRW and other IDE device (HDD) have same config (like both have primary slave or primary master). Check if the jumper in the CDRW is into SL or MA; place it in CS(Cable Select) mode so it doesnt clash with other IDE device.