Quick question i'm running 3.55 Kmeaw CFW and everything is working great, got bored playing and popped in a DVD (old school dvd) and it never showed up on the XMB the spinning clock thing did its thing and disappeared but nothing. I then put a BR disk in and that movie showed up just fine. its a 250 gb slim. Being i never tried to play a dvd on this firmware before, does it play them?
Should do, I'd try a regular audio CD then check your model number and see if your PS3 is one of the ones with 2 lenses (one for blu ray, one for DVD/CD). I've never had to repair a drive in a slim so I don't know off the top of my head. But if it does have dual lenses and no dvds are working (after trying a few) its probably just a dirty lens.
Just checked slims have dual lenses (source:http://www.hanger.org.uk/h/hangershop/news/14/What-PS3-Lens-Do-I-Need%3F.html). If no DVDs are working but CDs are I'd say the lens is dirty since DVDs would be more picky about the lens being clean than CDs and CDs are working so you know the lens isn't 'broken'
But it might be worth your while rebuilding the database before you open it. That has solved a few blu-ray reading issues for me in the past.