Not really an answer, but you could also try to clean the laser head yourself to see if this solves the problem (do not use alcohol as this leaves a "film" on the lens itself)
If this does not help you could replace the DVD-ROM for a working one (new or 2nd hand from eBay)
As for playing COD4 without the DVD:
http://m0001.gamecopyworld.com/games...f_duty_4.shtml