If you mean you lost bluray movie playback then yes that happens when you downgrade it's also well documented. There's currently no certain fix but a small number of people have had a bit of luck reinstalling firmware and things like that but i wouldn't hold your breath.
Yes you can still use acid, that wont give you bluray playback though. You can find a how to and all the relevant details in the acid cfw thread and I'd advise you actually read it fully not just the first post.
Unfortuanately you have a lot and I mean A LOT of reading ahead of you, since the downgrade was released the Blu-ray issue has cropped its ugly head up many times on the boards, some have had success by downgrading as low as you can and then upgrading to a stock 3.41 firmware, others have altered their system files in the PS3 dev_flash2, and dev_flash3 folders, this can be dangerous but has proved effective for some, and luckily some have not has this problem at all.
Although I did see recently that a group of devs are working on a project to restore Blu-ray playback completely on all PS3s but it is still a WIP I believe.
The key is trial and error, try everything one at a time, following the instructions to the letter, if you don't understand any point that the poster has made don't be afraid to ask questions, the community is getting stronger and everyone here is here to help.