PulseAudio shows playback but no sound through speakers or headphones

Two days ago I started using Arch Linux. I've got some sound issues. I've installed alsa, alsa-utils, etc., and unmuted all channels with alsamixer. My user is in the audio group. I've also installed pulseaudio and started it with pulseaudio --start. The command speaker-test -c 2 does not make any sound. In pavucontrol (I'm using i3, but I don't think it matters), it shows my sound card and the jumping line that indicates something is playing sound on it. When I plug in headphones, they are detected and the sound device switches from speakers, but still no sound. hwinfo --sound displays this:

20: PCI 1f.3: 0403 Audio device
  [Created at pci.386]
  Unique ID: nS1_.b28td23g3aB
  SysFS ID: /devices/pci0000:00/0000:00:1f.3
  SysFS BusID: 0000:00:1f.3
  Hardware Class: sound
  Model: "Intel Sunrise Point-LP HD Audio"
  Vendor: pci 0x8086 "Intel Corporation"
  Device: pci 0x9d71 "Sunrise Point-LP HD Audio"
  SubVendor: pci 0x1043 "ASUSTeK Computer Inc."
  SubDevice: pci 0x1a00 
  Revision: 0x21
  Driver: "snd_hda_intel"
  Driver Modules: "snd_hda_intel"
  Memory Range: 0xef528000-0xef52bfff (rw,non-prefetchable)
  Memory Range: 0xef500000-0xef50ffff (rw,non-prefetchable)
  IRQ: 130 (616 events)
  Module Alias: "pci:v00008086d00009D71sv00001043sd00001A00bc04sc03i00"
  Driver Info #0:
    Driver Status: snd_hda_intel is active
    Driver Activation Cmd: "modprobe snd_hda_intel"
  Driver Info #1:
    Driver Status: snd_soc_skl is active
    Driver Activation Cmd: "modprobe snd_soc_skl"
  Config Status: cfg=new, avail=yes, need=no, active=unknown

Yesterday I left my laptop turned on for maybe an hour, and sound started working, but only until the next reboot. Can anyone help?