A friend of mind played it first on his laptop and it worked fine.
...
I then tried to play it on my main desktop computer... it is not recognising the disc at all...
Well, since the disk have worked fine the first time, it mean that the disc was good... try again on your friend laptop and if it work, it mean that something is wrong with your drive... if it don't work, it mean that something bad have happen to the disk ( UV from sunlight, or humidity with rapid change of temperature, or ... ) between the use by your friend and your own test...
Anyway, you can always use Impulse for install the game ( need a valid serial and register the game )... version installed will be the last one... and since sins don't have any copy protection, you can perfectly backup these updated version on a DVD if you wish...