my laptop will not read cds/dvds

i bought my dell inspiron laptop around 6 months ago and the other day i was burning a few cds onto my itunes.  when i put the final cd in it went a bit strange and only managed to get through half the cd before freezing. i thought i was the fault of the cd so just left it.  then today i have just tried to burn another couple of cds ans the laptop will now not even recognise any cds or dvds that are put in the computer. what could be wrong? what can i do to fix it? thanks