Issues like this are covered by warranty, but if your warranty has expired, you can buy a bricked PS3 from eBay, or the like, and swap out the Blu-Ray drives. Whether that is a more feasible alternative to buying a new PS3 depends on how far away the bricked PS3 you buy is; over seas shipping tends to make it a very costly purchase, especially when buying things as large as a PS3 console.
The procedure of swapping the Blu-Ray drives isn't an awfully complex task, and you can find many, many references and instructional videos showing the whole process step-by-step on the web.
To appease to your actual question at hand: like Ekonion said, it's most likely a mechanical issue. Had the laser been broken, the plate would've spun up, and the PS3 would've reported the disc as unreadable or of unknown format.