DVD problem with Toshiba Satellite 1800-712

I have a Toshiba Satellite 1800-712 (1.1GHz, 512MB RAM, using Windows XP) and the DVD drive has only ever intermittently worked- sometimes for five-ten minutes perfectly- but then inevitably deteriorating into sticky/slow video and sound.

I have tried a number of codecs, a number of DVD players and even gone so far as to buy an external DVD drive, thinking that it must have been the one inside the Toshiba laptop causing the problem. None of this has worked.

Does anyone have any suggestions about how to fix this???

This ones 'a duplicate' so I've begun answering on the 'other one' ;)