But now I don't seem to have any audio output. Windows says I don't have a decoder or something.
Any clues?
Been away ski-ing so just catching up and I've had a similar problem, so check this...
Go to the root directory ( c:/ ) via My Computer and right click on C:/ then <Hardware> tab, select your CD/DVD player and click on properties.
Then, in the <Properties> tab for your CD/DVD device, check that the "Digital CD Playback" option is unchecked.
i.e. set your CD/DVD player to analogue settings (unless you feed your PC to HiFi audio equipment with a DAC/digital amp...)
It took me ages to find this out after I'd re-installed Win Media Player 11 updates... Some codec somewhere had over-ridden this. Or some numptie when they (ok, it probably was me) re-setup the system. You need the analogue signal setting to send output through the PC's sound card/devices. The digital output option will divert it direct to an output connector (such as an HDMI or S/PDIF terminal) bypassing all the PC's own sound devices.