After I disassembled and reassembled my laptop, I turned it on and there was no sound coming from the speakers. I thought I must have forgot to plug in the small speaker cord from underneath the motherboard, so I reassembled it again. I cannot say 100% that the cord was unplugged, because when I disassembled it again, I ripped the ribbon cable from the power board so I was distracted by that (the ribbon cable is sticky on one side and apparently it got loose and somehow it got mixed up with the DVD case, so when I pulled out the DVD case, it ripped the cable). After I was sure that the speaker cable was plugged in and after I replaced the ribbon cable, I reassembled it and there was still no sound.
When I open the device manager, I see a yellow exclamation mark next to Audio Device on High Definition Audio Bus. I tried updating/installing it, but it says:
"windows found driver software for your device but encountered an error while attempting to install it.
High Definition Audio Device
The system cannot find the file specified."
I went to the ASUS page and downloaded Realtek High Definition Audio, but again, no change.
Also, system sounds are OK, e.g. when there's an UAC notification.
Thanks for all your help!