Lite - on SOHW 802S

Hi, ive got the Lite - on SOHW 802S DVD/RW drive its been working fine for the last 3 months but now i insert blank cd-r discs and it detects them i put in dvd - rs and it doesnt detect them and i havent changed the discs i have been using. any ideas on what the problem is and / or the way of repairing it.

Many Thanks.

P.S - or is the drive completely knackered ???